Oh the ending’s gonna be bittersweet for sure, I just don’t see the remake not leading to AC and DoC as somehow undermining them. Those stories have their place in canon, they’ve already been told, and like I’ve said probably a dozen times already, they will always be the canon follow-up to the OG.
And there's literally no other reason to do it than to "brighten things up," so to speak. It certainly isn't required to provide a resolution to anything. The cliffhanger from Dirge's secret ending could be addressed here in the remake series, just as the question of what became of Sephiroth's consciousness after AC is seemingly being addressed here.
If your concern is then "What about Dirge's secret ending and Sephiroth's consciousness after AC in the remake timeline?" -- maybe the same thing happens again? Maybe the Whispers end up restored before all this is done, and the consciousness of the present-day Sephiroth from Universe-B will someday (in the far, far future; long after Universe-B's AC; on the edge of the planet dying) cross over from Universe-B to a Universe-B2? And then precisely these same events will play out again? And then it continues on and on across timeline after timeline into always?
I could see that happening both as a way to give Sephiroth a slight victory of sorts of his own, where he realizes he will never end even though he'll be eternally defeated ... but also to punish him in the worst possible way, as he realizes he will be eternally defeated by Cloud. Contained to a looping causality prison of his own making because he wouldn't let himself escape his own history of pettiness and self-sabatoging behavior.
And let's be honest, who here really thinks a cross-dimensional causality loop (not really a time loop -- just a looping of events across different, ever newer timelines) is too convoluted a trick for these guys to pull?
But for me ... thematic resonance put aside ... Sephiroth's just desserts aside ... even "Nomura's gonna Nomura and Kitase's gonna Kitase" set aside ... the biggest reason I believe what I believe always comes back to this:
I really don't see this thing ending in any way that doesn't lend itself to Square being able to reissue AC(C) for the 12th time on 16K Ultra HD Holodisc or some shit with marketing like "See the hit sequel to the most groundbreaking gaming adventure series of the past decade (because they've been coming out now for a decade) -- FFVII Remoded!"
At the end of all this, you're going to get an ad telling you to revisit the next stage of the Forever Crisis in FFVII: Advent Children Complete. Mark my words, people.