VIII to me is the only game in the series that seemed to have plausible sequel ideas. The world is one of the more underdeveloped and it was one of the few games that had reasonable plot threads left open afterwards that get glossed over by its unrealistic sugar coated ending.

Ulti is dead and despite the world governments being in shambles and the most powerful empire in the world coming out of isolation (which we all know should start a global panic) not to mention Garden and SeeD are in shambles we just kind of end it with smiles and cheers when there was a a lot left over to talk about.

Despite all this, I hate the ideas of sequels and prequels and would prefer the series to stay to the one game world instead of expanding into crappiness like VII and X did. Even the Ivalice games are making me hope for the franchise to die lately and I genuinely loved FFT and XII.