I love and adore Pinocchio with all my heart. I even own it, but don't watch it all that often for whatever reason, but every time I do, I'm always reminded of how truly great it is/what a true classic it is. But I don't know how it would translate :/ The Golden Age films weren't created with "stage" in mind. Pretty much all the musical films Disney has ever made have at the very least, a SLIGHT stage essence about it just by being a 'musical' or 'movie with music' as I think the Golden Age ones are, but not every Disney movie musical would translate/read on stage well. Tarzan and Little Mermaid being the two Renaissance ones that def didn't need to be on stage.
Pocahontas is the same way but for different reason. Even Menken has said, he doesn't know how Pocahontas would translate. Pocahontas, I believe, was meant to stand on it's own as a piece of race relations commentary as a film. It's theme, I think, keep sit from being a good stage property. It was created to tell that always relevant theme, and that's it. At least, that's my bets explanation. Sometimes you don't why something won't translate, but you just know it won't. Allegiance I daresay flopped for the same reason. These themes are better told in other mediums rather than a stage musical. Musicals just by being musical live in their own world and still need to entertain as well as educate as make us "feel".
Now why Hunchback works in most mediums, I think it's because the story has that sweeping epic feel to it already. It lends itself to being a musical tale well. And of course, Menken just made it even more epic and sweeping with that God sent music of his..."Bells...Dame" is still my musical crack yo.
And speaking of, He HAS said more than once when asked about which is his Disney works he's like to see on stage, he's answered with Hercules. I'M STILL WAITING ON THIS!!