CZJ would be hilarious as the Chaperone, plus she could probably sing it better than any of the others mentioned. I'd love to see her stagger around, saying "Where's the bar?"
They will need another movie star (preferably one with box office clout) besides Geoffrey Rush to really get the backing and push that it needs. I'm sure he knows that.
There's always that go-to gal, Meryl Streep for the Chaperone. She's in every movie now.
Janet and Robert will be tough roles to cast with big stars. "Show Off" will put a lot of actresses out of the running. And how many younger male movie stars can tap dance? Yes, you could cut his dancing, but you're starting to mess with what makes this show-within-a-show special if you dumb down the roles.
We shall see. I'm hoping Rush gets a big name for the Chaperone and casts competent (relative) unknowns for the other parts. It's a small cast, so that helps. I think it could be made fairly cheaply.
The other thing that would give it a boost is a "star director." Martin Scorsese should do it. One of his many New York movies, from yet another perspective.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22