11-16-2015, 12:21 AM
I'm pretty sure that Square-Enix and Disney are highly protective of Kingdom Hearts as an intellectual property, and I don't think they'd allow it to cross over much with other stuff. In the future, though, if there ever is a time when characters who did not originate in video games could be included in Smash, Kingdom Hearts would probably be a prime candidate given that most of the supporting cast are straight up Disney characters.