I'd love a spin-off for Final Fantasy VIII. My favorite regular game in the series(that wasn't some other genre, that is). I mean, I like a lot of the other ones too, but this one took my fancy, since it rewarded smart play and combinations(of equipment and spells), not just power-leveling.
Not that it isn't a solid game that finished well, but something set in the same universe, perhaps. Or based around some of the characters. Seifer spends a lot of time away from the group, Irvine isn't met till quite a bit into the game, basically stories based around characters who could spend more time being delved into.