The big argument that people have against including Marvel and Star Wars is that the universes are too big to organically incorporate into Kingdom Hearts. And for the most part I agree, specifically in reference to KH3. There's a hell of a lot of plot to get through in 3, what with unfolding the ramifications of Xehanort's machinations and the complications that 3D added. Plus outside of the original Mickey gang and the Wizards, (and to a lesser extent the Princesses), Disney characters only come from movie worlds; cameo duty is the domain of Square.
That being said I don't think they should be excised entirely. What I think could work is using Big Hero 6 and Star Wars Rebels: Spark of Rebellion. That way you can do the same thing as has been done before (Disney movie based world) and you get the added benifit of the tighter narrative in which to insert Sora. Plus if the story is like in KH2 (visit once for Disney, twice for Square) the second visit can be used to draw in the other universe characters like Spidey, Luke, and the like.
How would you like a Rebels and Big Hero 6 world?
That being said I don't think they should be excised entirely. What I think could work is using Big Hero 6 and Star Wars Rebels: Spark of Rebellion. That way you can do the same thing as has been done before (Disney movie based world) and you get the added benifit of the tighter narrative in which to insert Sora. Plus if the story is like in KH2 (visit once for Disney, twice for Square) the second visit can be used to draw in the other universe characters like Spidey, Luke, and the like.
How would you like a Rebels and Big Hero 6 world?