That kind of depends, it'd have to be a KH game where it'd be for online only, and that you could custom characters yah? I mean, like all of the KH worlds, but all of these custom keyblade wielders wandering around. Yes, that'd be a cool. But a basic KH game with other people sounds... annoying.
1. You are a person who is trying to survive the times of chaos caused by the heartless
2. keyblades are either impossible to get, or extremely difficult to get (I.E, A long quest)
3. Multiple classes and the traditional method for choosing what your character looks like
4. Larger and more worlds
it might not suit the online world that well, but it would be AWESOME if u could go online with it. just think, actually battling someone besides the computer, or make a party with other people and take on the Heartless. Now doesn't that sound good. And lets not forget the gummi ship. If you cluld fly around and try to blast eachother or the Heartless out of the sky, that would be pretty cool!
ok edit to my last post... i agree that it is best suited off-line, but if it were to be, Sora, goofy, and donald would be in the game, but they would be unplayable (Ex.Leon(Squall),Yuffie,Aeris) and you would have a customly made character, and Keyblades and/or other weapons, could be customized in looks and in power, and there would be all the same worlds +, but thats just my opinion, yea and i agree with making partys with other characters, but i still think its best suited off-line.
i really wouldn't care if it was online as long as it could be played multiplayer from the same console. a lot of people can't afford to play online and aren't able to have the same experience as the other people do. at least have it multiplayer on and off-line.