So it's kind of like...it would be set over a MASSIVE time scale, unbelievably long. And (we'll just call them humans for now) the humans, in the time between X and VII, got into space, founded other planets, lived there, and lived there so long that they forgot they had ever come from other planets? (Maybe due to some massive destructive event.)

It's plausible, I suppose. One of the main themes of so many Final Fantasy games is the idea of technology going bad and destroying everything, thus why so many of the games are set in this kind of post apocalyptic world in which everything is run down and back to ancient times kind of, but with some leftover technology still being used etc.

It's a cool idea though. I'd go in for it.