Nomura has said that FF is playing only a cameo role and that FF will never have a real world, like the Disney worlds. Usually the FF characters are associated with one of the non-Disney worlds like Radiant Garden.
Honestly, the FF characters are kind of a moot group of characters and I feel games like 358/2 and BBS who either removed them entirely or only have one minor cameo have sort of proven the series really doesn't need them in the games cause they actually don't really do anything besides fan service. I actually wouldn't mind if Squenix just decided to finally purge them from the games entirely cause its not like Cloud or Squall have actually been doing anything relative to the story in any game they are featured in beyond the very first game.