I have heard this conversation numerous times as when Brawl was being created, Sora was highly sought after character and originally, Brawl was rumored to have 3 3rd party characters, and at the time, Sakurai was creating "Project Sora" which people mistook for thinking Sora was a character in the game, which turned out to be false. Anyways, Sora would be a really good fit into the SSB series and I don't think Disney would not allow them because of SSB's huge success and because SSB isn't very violent, but more associated with being family-friendly.
Sora's colors would obviously be his forms and his gameplay wouldn't be too difficult either. He doesn't need to have many magic attacks and could probably stay true to his KH form if he had one or two magic attacks. His Final Smash I won't delve into but I could see a Trinity Limit final smash. The thing is though, I'm not sure why, but I would rather have Roxas in SSB over Sora.