"I can't think of any composer that I would want to hear adding additional material to Tchaikovsky."
All you need is a great lyricist and musical director to make new songs. Adapt more music from the ballet - maybe expand on it a little a la Preludes. That would make the score sound a little more cohesive than bringing a new composer in. Also, there are songs that got cut before the finalized version of the film, which is less than 90 minutes.
The problem is Disney loves to pander, and they would want to add a funny song for Maleficent. That delineates from what the film is - a beautiful classic that took extra measures to look like a picture book. The show would need to be done in a classic (1950s) style that fits the tone of the film. If done poorly, we could end up with another "Little Mermaid" - a good score that doesn't form a cohesive whole ("She's In Love", "Positoovity" and "I Want the Good Times Back" are good songs but they sound nothing like the film).
"Sticks and stones, sister. Here, have a Valium." - Patti LuPone, a Memoir