SPOILERS AHEAD
Listen I get you say you are dooming or being negative. We’ve all been there even in things unrelated to Final Fantasy VII or gaming in general, hell I can be a pessimist in real life for sure…
Your feelings are valid in this case, especially when they’ve fed LTD stuff in the past, but I don't think you are correct in a lot of what you think could happen, let me explain.
For starters let me preface this by saying, I think a lot of people struggle to seperate the blurred lines of "feelings" between characters in media, especially when they are complicated or expressed in ways that we wouldn't necessarily express these feelings ourselves, let me give 3 different examples.
Liking - The basic form of being interested in somebody, either platonically or romantically. (e.g Aerith not knowing what kind of "like" she likes Cloud. Cloud liking Barret as a friend and so on)
Love - The secondary form of being interested in somebody, either platonically or romantically. (e.g Cloud loving Zack as a friend and brother figure or Tifa loving Barret as a friend and father figure)
In Love - A completely seperate form of being interested in somebody, probably the highest you can express, this can only be in romantic form. (e.g. Aerith and Zack being in love with each other during their relationship and Cloud and Tifa being in love with each other since their teens. I don't think either of these is a reach considering all the material we have to go on.)
1. Cloud's reaction to Aerith's death (as well as in relation to Tifa's "death")
Now I don't see this as out of the ordinary at all, let's assume for a moment he has the same exact reaction in the OG, except the parts like the speech which he has blocked out in Rebirth. The only reason you don't see this in the OG and we can feign ignorance is because of the lack of graphics, animation and voice acting, but suffice to say i'm sure he is just as upset in the OG as he is in Rebirth, yet everything that happens in Disc 2 still happens regardless. Now why wouldn't Cloud be upset? For starters we play the game through the eyes of Cloud for the most part, we bond with him and feel what he feels because he's our gateway into the story and the lives of the characters.. it would be a failure on the part of the creators if we felt none of the pain or anguish Cloud feels and this is just as true when Aerith dies, because we are shown that whilst yes in Remake and Rebirth he can be quite abrasive towards Aerith and doesn't seem to reciprocate any flirty banter or potential interest, he can also be caring, understanding and comforting to her as well. This is because he loves Aerith even if he doesn't necessarily know this when the moment happens, yes I said loves, I know it's a scary word for shippers but it is the truth, but look at my definition above I don't think it's wildly out of pocket to say Cloud loves Aerith, maybe as something more than platonic but not quite so far enough as to be extremely romantic. What would you do and how would you feel if you tried to save somebody you loved only to instead see them brutally slain infront of you and you failed to save them. (Think his Mom, and especially what happened after losing Zack too.)
Now let's contrast this with what happens with Tifa earlier in the game, true, Cloud doesn't cry or get angry or anything like that, we do get the initial sense of disbelief and anguish as he cries out her name... but beyond that he immediately does what he has always done when his emotions are in turmoil when it comes to Tifa, his weaknesses are exploited (Sephiroth stepping in to exploit Cloud as he tries to save Tifa), his defenses are down (he becomes vulnerable as he regresses into a more vegetative state), as he becomes non verbal and unable to even move. It is only through a hard punch and Barret saying Tifa needs Cloud again that he is able to find the strength to even stand and walk almost drunkenly towards her. After this, we then get a cutscene where i'd argue we see a big glimpse of realCloud and he becomes the most open and vulnerable we've ever seen him up to this point, partially because he thought he'd almost lost her. Now a lot of this is because of the connection we know Cloud and Tifa have and how big of a role she has in his heart, her role in helping to make Cloud whole again, it harkens back to Cloud's state at the train station before Tifa found him, and it harkens back to the state the other Cloud is in in Zack's world, where he hasn't met Tifa again.
2. Aerith in the Lifestream sequence (instead of Tifa)
This is one I don't particularly understand, although I can see where you are coming from.. I wouldn't rule out the prospect of Aerith appearing in the Lifestream in some shape or form, even if it's just to guide Cloud and Tifa and protecting them from mako poisoning and such. But the idea of Aerith being the one to make Cloud whole and "fix him" so to speak with Tifa being erased from the equation as a whole just makes absolutely no sense from a narrative or character perspective. For starters I feel like a lot of people have either forgotten or don't fully understand what the Lifestream sequence even entails, it's not a best hits collection of Cloud's saddest memories or biggest failures which anyone can replace Tifa in helping Cloud get over them. It's a realisation that the Cloud we've come to know and understand was never the real Cloud all along, that we've been playing as not only an extremely unreliable narrator but a combination of different personalities stuffed into a Cloud shaped shell, with the real Cloud bursting to break free. Genuinely what purpose would Aerith or Aerith's death being shown in the Lifestream serve to restore Cloud back to the real Cloud? The narrative and characterization demands that Tifa can be the only one to help Cloud piece together what he has lost for two reasons.
2.1 - Because she is the only one in the party who has even met the real Cloud.
By Aerith's own admission in the games and even the side materials such as the novels, she never met the real Cloud, try as she might, up to that point... it would be impossible for her to help him in this regard. Hell you could make a better argument for Zack helping Cloud out than Aerith, he at least knew the real guy for a while. However Tifa is the only one that is able to confirm to him that he existed as a person before what happened at the Nibelheim mansion because she knew of him and his mother from childhood, and is the only one able to combat Sephiroth's gaslighting in this manner. Zack also would not work because of the next reason, which even Zack himself knows.
2.2 - Cloud is in love with Tifa Lockhart, not Aerith, they share mutual feelings, and he has buried these feelings deep within his real self.
Watch the OG Lifestream sequence where they confirm mutual feelings, read the novels such as TOTP (Tifa loves and wants to spend her life with Cloud) or the recent 2,000 Gil Cloud short story (Cloud wanted to become someone special to Tifa) hell just experience all that FF7 has to offer and there's no way anyone can deny this fact, even if they try to convince you otherwise. Cloud's whole motivation at this point is to become what he considers as worthy to be with Tifa because he's in love with her, with the irony being that Tifa never wanted or needed Cloud to become something he is not to be with her (TOTP) but of course both being shy they are unable to fully convey their feelings at the time. Thus a big part of the reason Tifa is the only one able to piece together real Cloud is because whilst he himself may be fragmented or 'hollow', his feelings for Tifa are something that have remained evermore. This is the reason you see his different physical and emotional reactions to and with Tifa throughout the games, even if they only happen subconciously. It's not a coincidence that Nomura himself said that real Cloud is somebody that only bubbles to the surface when he is around Tifa. This is why such scenes as the Lifestream exist in Gongaga -- This is the devs showing us that the planet considers Tifa important enough to protect her from Sephiroth and show her who real Cloud is because it knows the role she is about to play in restoring Cloud in Part 3, it's foreshadowing at its finest.) -- Consider as well that Tifa's precious memories consist predominantly of Cloud and vice versa. To replace Tifa here with Aerith would take a considerable rewrite and redefinition of the Lifestream sequence concept as a whole and remove a large and important part of Cloud and Tifa's carefully crafted arcs that intertwine with each other.
3. Cloud and Aerith will be canon in the endgame of the Retrilogy
Now this I can see why you might feel this way, for starters there is a lot of (mis)information going around the internet about a lot of things in relation to the 'LTD', what's optional, what's canon, who said what, in what language, who's in the credits, who knows Japanese culture better etc etc. It's all quite exhausting and quite frankly annoying but the internet will internet and it is what it is. I'm going to present some points as to why I think not only will this not happen, but would be extremely negligent and destructive for the devs to do this at this point.
3.1 - Hollow and NPTK
The discourse around these songs has been going since Remake and up until a week or so ago nobody would shut up about NPTK especially. But here's the thing,the developers have confirmed that Hollow is a song about Cloud's feelings, and the developers have confirmed NPTK is a song about Aerith's feelings. What they haven't specifically stated (to my knowledge) is that they are songs about their feelings towards each other and each other alone and there is a distinction between these two things. We already know from what happened last week that Nojima himself spoke on camera -- and later doubled down in a tweet -- that NPTK is a song about all of the people Aerith has loved, loves or who she has come to love through her life's journey up until this point, knowing that it likely isn't going to last much longer, yes this does include Cloud but it also includes Zack, Tifa, Elmyra, Ifalna etc. No amount of essay's, harassment, crying or otherwise will outweigh the words of the person who created and wrote the song as well as wrote the story and scenario of the Retrilogy and has been involved in the world of Final Fantasy VII since it's inception. As for Hollow, whilst we haven't had such a confirmation from Nojima or anyone else, suffice to say Cloud referencing being 'Hollow' in reference to forgetting who Zack was and losing himself to degredation, as well as the song itself playing in the Badlands where Zack died should be all the confirmation you need to know that the song is about more than just 'Cloud's undying burning love for Aerith and his wishing to be with her forever.'
3.2 - Cloud and Tifa's budding romance
In Remake if you didn't feel the tension and desire from both characters for each other then you were either being willfully ignorant when playing it, the constant need to touch each other, flirt, have serious conversations, parallels between saving each other etc etc was already pretty phenomenal stuff. Hell even Aerith -- before losing her memories -- seemed to engage and encourage the connection between Cloud and Tifa herself. Now on top of this, rather than think to themselves, okay we know we're going for a Cloud and Aerith endgame so let's tone down the Cloud and Tifa stuff and make sure we establish Cloud and Aerith as the true pairing, they instead doubled down on the Cloud and Tifa connection and decided to up the ante considerably. More touching, flirting, hugging, angst, romantic tension you could cut with a knife, a nearly kiss, an actual full on kiss, hand holding... Cloud fantastising about multiple Tifa's, Cloud and Tifa constantly touching and reassuring each other as they begin to feel lost in their trauma's, Cloud constantly staring at Tifa, Cloud's reaction to Tifa in a bikini with her music in the background, Cloud confirming mutual feelings on the Gondola, Cloud holding Tifa's hand during the NPTK performance, foreshadowing of the Lifestream sequence, references to the flower on Tifa's doorstep, their connection, extremely well crafted body and facial animation showing desire between the two or them, cinematography and camera work showing Cloud POV focusing on Tifa on multiple occasions, literally seeking her out in a crowd. I could go on and on, their whole arc in Rebirth is basically 'Romantic Tropes 101: A Guide to Crafting a Romance in Media' you can reference umpteen amout of films and literature when it comes to the beats of the romantic storycrafting in this game between these two.
3.3 - Cloud and Aerith themselves
As I mentioned above, Cloud does love Aerith (in my view, platonically), at least you might figure he does by the end of the game, and we know for certain Aerith at least likes Cloud (at minimum loves in a platonic sense) but she isn't sure if this is romantic or platonic, and unfortunately for her she never gets the chance to find out. They have some really nice moments in the game that is for sure, to say they get absolutely nothing would be a lie, or you've just skipped a lot of Aerith stuff on purpose. But here's the kicker.. in comparison to what we see from Cloud and Tifa, is there anything that Cloud and Aerith does in the game that could be considered extremely out of the ordinary for two people who love each other very much, just not romantically? Because I would argue kissing somebody is a sign of romantic love where as holding somebody's hand (fingers or not) might indicate there is something there but there is enough ambiguity to say well.. it's not a kiss so where does that leave it, context is key after all. I've mentioned above that actually Cloud can be quite abrasive towards Aerith at times, especially when she becomes overtly friendly or flirty (Costa del Sol for example), she also has to grab him constantly against his will as he's not so fortcoming (Grabbing his arm on the Gondola, where he even questions 'Aerith?'), and they never seem to be in step with each other in this regard. Now you can argue that is her personality and that is fine, but consider the initial Gold Saucer date when they attempt to go on the Skywheel for example. Both Aerith and Yuffie immediately grab Cloud's arm forcefully and try to drag him forward onto the wheel where it quickly cuts to it shutting down, in comparison to Tifa who carefully holds his hand and checks to make sure Cloud doesn't want to back out of it before proceeding forward where they are in lock step with each other, where the camera lingers a moment longer on the two of them walking forward before cutting to the Skywheel cutting forward. There's a lot more I can say here but this post is already extremely long.. the only other thing I will say is consider the Church confession and the S5 date.. leaving the Zack parallels out of this as i'll mention him in a minute, consider that the S5 date went horribly wrong from all angles, and consider that whilst Aerith was confessing she liked Cloud in the Church but wasn't sure what kind of like that is, Cloud hasn't once reciprocated any romantic intent towards Aerith throughout the entire game, he hasn't kissed her, hasn't affirmed any mutual feelings, hasn't once encouraged her or led her on to be romantic in any way. Hell even at the end after everything has happened all they have is some friendly banter between themselves, zero romantic confessions or physical contact. I'm also not gonna get into the romantisation of what heppsn at the end because quite frankly it's stupid. Please I welcome anyone to correct me with evidence if I'm wrong on this. Instead what we do get at the Church is there is a possibility for Cloud to even call Aerith specifically a friend (in the Japanese dub) and regardless of what Cloud says Aerith gets her closure by confirming that she knows where her and Cloud stand now.
3.4 - Zack
Some will say there is a lack of Zack and Aerith moments in this game but I don't see that at all, there's plenty enough for a big pay off in Part 3. I'm not going to get into this complete because I made a post a few pages back about Zack and Aerith. Suffice to say in the game Aerith herself confirms she still has feelings for Zack, she herself even shows throughout the game she is conflicted about her feelings for Zack and what could be potentially something she feels for Cloud. Zack's sequences also show him totally devoted to Aerith, they touch hands through the lifestream, they look up at the same sky as the scene cuts to Aerith from Zack, Aerith helps Zack out at the end multiple times and Zack ends up in a church with flowers blooming talking about reuniting again. Like do we honestly think they would reintroduce Zack only for Aerith to cast him aside for Cloud immediately? That they'd show us Zack getting his heart trampled on for some reason? That Cloud would remember who Zack is and how in love he is with Aerith only for him to immediately pursue her? It's a crazy notion and one the writers won't indulge, they aren't writing a Netflix high school drama here.
There is so much more I can say on each point, but I'm going to wrap this up because it's already an extremely long post and I imagine people rolling their eyes when they see posts this long. Suffice to say as i've mentioned many many times before, the time to push for Cloud and Aerith endgame was from the very beginning of Remake when they were first writing this whole Retrilogy, because you could write a compelling Cloud and Aerith romance into the game without having to assasinate your characters and change and belittle huge parts of the story that has existed since 1997 that way. That never happened however, and maybe you could make the argument that okay, Rebirth is now the time to solidify that Cloud and Aerith endgame because this is their moment to shine, as it was in OG, we haven't gone too far down the rabbit hole in Remake that we can't rescue this.. instead they decided to double down, make Cloud and Tifa kiss, show Zack caressing Aerith's cheek and crying over her in the actual opening scene and everything else i've described above. Now we are 2 games into a trilogy and we already know a lot of the things that happen between Cloud and Tifa in this next part. Everything they have created so far now means that for Cloud and Aerith to be endgame in part 3 the devs would have to trample all over the likes of Cloud, Tifa, Zack and Aerith as characters, but also pull out threads, rewrite and basically besmirch the very story they've carefully crafted up to this point. This could have all been avoided had they planned for it since Remake, but they clearly haven't and now they've basically cornered themselves on the direction they can go with this, which is Cloud and Tifa and Zack and Aerith. Cloud and Aerith romantic endgame at this point would be changing the game and it's characters so drastically it might as well not be the third part of the Retrilogy, hell it might as well not be Final Fantasy VII at all, but some kind of canon AU project to please a certain subsection of fans.