endgame is obnoxious but it confirms a things:
* Again this is sequel hidden in a remake.
* I have a theory on the ghost past preserving the FF7 timeline - I think the ghost are a metaphor for memories of FF7 players. The ghost are us.
* They are clearly getting the key aspects of FF7 out the way quickly. All the major aspects of FF7 have been referenced in some way. I sense that the next part could be drastically different and the possibilities are exciting. I love how the ghost drag Hojo out the room before he could reveal clouds secret out in a very *nope to early* fashion
* game is like Fuck Wedge
Jumping on the meta-commentary bandwagon just like most everyone.
There's quite a LOT that they haven't touched. But to see any of it, you have to play it as the game being standalone, and as if you've never played the original. Because the game, while having been made for fans, was also made for newcomers. And as such, playing the original isn't required.
So many people do as you do and keep making references and links to the original, as a sequel, that include time traveling , multi-dimensions, or anything like that. But if you'd try to take the game in isolation instead of linking it to the original, you could come up with other conclusions and theories that are far more grounded than those Kingdom Hearts shenanigans.
That being said, nothing will be known for sure until S-E releases information about the sequel.