I'm fairly sure the PS5 - if any - will be an incremental improvement over the PS4 - that is, unlike the PS1/2/3, it won't have any weird hardware, just off the shelf components from (probably) AMD. That means the main difference between PS4, PS4 Pro and PS5 will be turning knobs for graphics settings, maybe texture resolution (because as RDR is showing, games are getting HUGE). Ideally they'll be able to tweak the settings so that there's acceptable framerates on all systems.
PS 5 or PS Pro+ will be focusing on getting stable framerates on 4K and / or PSVR. I'd personally be happy enough with just a stable 60fps on HD myself tbh, the PS4 can't manage that in a lot of games (and in some cases / games the PS Pro can't either when rendering on HD - poor optimization).
I’m guessing this is why many users here think it will be on PS5 and skip the PS4, coupled with lack of news - which Nomura has been denied and Square only wanting to market KH3
People can often think “oh new console, new graphics” but it’s more than that. If they have skipped the PS4, which I personally don’t think they have, for Part 1 anyway... they would be able to be develop the game for more powerful hardware, that allows more objects on screen whilst keeping a stable frame rate for example... rather than remastering it or upgrading it later.
Since this topic is Remake Story/Content Hopes, may aswell stay on topic and just state that some of the Story set pieces will be able to be grander on PS5 than PS4, since the PS4 hardware is old in comparison to 2018 hardware you can get, it wouldn’t exactly be shocking to hear that newer hardware (PS5) can deal with more things going on at once than PS4 hardware.
In terms of Part 1, I hope they really catch the theme and vibes of the events that occur in midgar throughout the game, PS4 or PS5...
And hopefully they get the voice acting correct to capture the emotion during said events.