To be honest, I can't imagine a Marvel x KH crossover working out.
But that Spider-man and Disney comparison that Mirby made has me intrigued. It definitely could fit well.
Yep. Disney's much, much more than just movies. As stuff opens in the way of more fan-loved and reasonably unknown (at the time) stuff like Tron, and more recent stuff like Chicken Little (not to mention already having stuff from a direct-to-video sequel), it could definetly fit in properties like Duck Tales and Gargoyles. And things happen in ridiculous, mysterious ways. If Disney sees the amount of success and moolah that Capcom is making with the MvsC franchise, why not allow a few more crossovers? For money's sake, since Marvel can go child-friendly when it wants to.
... Nomura also won't allow Marvel in. Trust me, there's no way in hell that Marvel is gonna make it into KH; it was founded on using strictly Disney's original properties, and that's not gonna change anytime soon. You can dream all you want, but it won't happen in a million years.
Why wouldn't he? Japanese people love Marvel. And what is an "original property"? Disney has thousands upon thousands of original properties, some quite unknown, and some not directly Disney. Like Nightmare Before Christmas, which was released under the Touchstone Pictures banner, only recently switching back to Disney. Heck, Kill Bill is an original Disney property, the company certainly created it.
So Nomura notwithstanding, since he's the head honcho of the series but the big heads in the company have the final word, in a time when the Marvel movies are coming out in quite alot of popularity, and a time when a rival company game has quite a bit of success with a Marvel crossover, what's stopping Square from requesting to use Marvel in KH? Even better, what's stopping Disney from saying they can use the Avengers movie properties, making the game yet another very successful tie-in? Money talks. And Disney does stuff for money nowadays.