MACK & MABEL
INTO THE WOODS
WONDERFUL TOWN
BILLY ELLIOT (the musical version, I know it's absolutely ridiculous to say since the story obviously works on film and I actually love the original movie, but I think the musical would work beautifully on screen)
FOLLIES (I think it could be a one in a lifetime film if it had the right budget and a really visionary director like Baz Luhrman or Darren Arronofsky at the helm, but this will never happen)
I completely disagree about SUNSET BOULEVARD. The Broadway show is a mediocre adaptation of one of the most brilliant films to come out of the Classic Hollywood period, on top of it the show is basically a replica of the film.
Also, I'm with CATSNY re a MISS SAIGON film, don't think it'd work without all the bells and whistles of the original production.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"