idk man, theres alot to think about rly. i mean kh is a rly story driven game at its core. i wouldnt say to the point of a final fantasy game but enough that it might make it awkward and hard to put in which in turn might feel like something that was forced rather than it blends with the game.
with 358/2 days the reason that it works is because the organization is a team, and they work together and such. a co op mode might work a lil in bbs on some moments but since we already know they go on their journeys alone i dont see how that can work. but who knows