I doubt Disney would put in Marvel into the game because they did allow Marvel too keep their movie and video game rights...so when it comes to video games...Marvel's video game branch (not Disney Interactive) does have a say, and I think if the idea was proposed the fanbase would have extreme opposition too it so they would decline.
On the topic of Disney running out of ideas, as much as I don't like to admit it, it is true...the classic Disney movies are running out...however, I don't think they would switch Disney after KH3 because there are still a few Disney titles that have not made their own world, and Pixar movies can rack up quite a number of worlds. Not Pixar, but at least Disney too name a few:
- Pinocchio (Days didn't have it in the final product)
- Dumbo
- Princess and the Frog
- Tangled (possibly...small chance but it is a princess tale)
- Enchanted (the cartoon world, not NYC)
- Fantasia (they could do something like that...utilize many different character in fantasia to create a stunning looking world)