I'm late for the Sora talk but I'll drop my two cents anyway.
"Sora wouldn't be well represented without Disney, you can't just have him in Smash without Donald or Goofy!"
Just like we can't have Cloud without Tifa or Barret... or literally any content besides his stage. KH has plenty of original worlds to use for a stage, Destiny Islands, Traverse Town, Hallow Bastion, Twilight Town, The World That Never Was, etc. Those worlds also have plenty of original music not like Sora would get more than two tracks. Sora has so much to use for a moveset that doesn't involve Donald or Goofy as well, and no RPG character in Smash just has their party members hanging around anyway, they only ever show up for final smashes and Sora has the perfect option for that with his keyhole blasty thing without Dolan and Gooby. There's plenty of original characters for a spirit board as well, Kairi, Riku, Roxas, Namine, Ansem/Xehanort/Xemnas/whatever, Organization XIII...
Not to say that Disney won't stop him anyway, it'll be a cold day in hell before Smash gets Sora from their grubby claws, but if anyone can do it, it's Sakurai...