I think some of you need to think about how something can actually be applied to stage, especially in terms of a musical. There are physical boundaries and time restraints (and the patience and amusements of the audience) you have to take into account.
A Cars musical? Oye vey. How do you suggest they do that with live performers? And on a stage? With racing? It works for film, but you can't do the same sort of things on stage.
A Toy Story musical has already been done, created for the Disney Cruise Line. I haven't seen it myself, but I believe Kevin Yee did a review on it not too long ago. He didn't like it all that much. Granted, "You've Got A Friend In Me" is not the best starting point.
You can't do the Muppets without the real voices, IMO. Or get exceptionally good impersonators.
If you're going to do a musical based off of a Disney film, I'd suggest looking at films that are musical-based. Beauty and the Beast, The Little Mermaid, and Aladdin certainly are. The music composed for those films were written by people that actually write Broadway musicals, so they know what they're doing.
Now, as noted, Peter Pan originated as a play. Many versions have been created, including musicals. I think this would be an excellent idea, and would prove to be very popular. The biggest problem I see would be the fact that you have children that are the main characters. You'll also have to break it to the audience that they won't get to see a human performing as Tinkerbell, since in the plays, she's just a ball of light.
Little Mermaid can't really be done because it's on Broadway, and the same goes for Mary Poppins and The Lion King. If anything else, Disney does not want to compete with itself.
Mulan could be quite beautiful as a musical...it could be incredibly artistic, reminiscent of how creative The Lion King is. Asian theatre is very rich in diversity and beauty - the more complicated scenes in the film could be solved (though you can't have real fireworks on stage), similarly to how The Lion King solved many of it's own problems visually.
Sword in the Stone would have a ridiculous amount of physical limitations...not sure that could be done.
Hercules would probably translate well. The only issues I can think of off the top of my head are Phil and Pegasus (in terms of physicality).
I think DLR has enough Nemo...and why can't the parks have their own, unique offerings? Not everything should be replicated all over the place.
Princess films tend to do very well with the public, so that's another thing. Cinderella could potentially do very well. That's been made into a musical, too after all. Not just by R&H, but Disney made something similar to Cinderella 3 (I think) for the Disney Cruise Line, too.