I think The Baker's Wife and Pippin are both terrible ideas for a movie musical. The Baker's Wife was a problem on stage because there is so little to it. Some really terrific music, but no real plot. I saw it in London and can't say that I enjoyed it very much, despite loving the score...it was just sluggish.
Re Pippin, it was always as light as a bubble. While the score is enjoyable, it still has a lot of filler. In 1973 it benefited from Fosse's direction and the first TV ad that was actually really good. Ultimately, there was a lot of 'stage magic' that made it a hit; but it is so light and episodic. I just don't think would lend itself to being a real movie...maybe it could be approached like the show within a show in Kiss Me Kate. Create a movie about the creation of the Pippin musical, and have highlights from the show built into the structure of the movie.
The musical I would love to see as a film will never be filmed because the show was a mega-flop is Rags. I know that Schwartz only wrote the lyrics; the score was written by Charles Strouse, who had some big hits, e.g., Birdie, Annie, and a lot of flops, many of which he provided really good music for, e.g., Superman, All American, Rags. I listen to the cast recording for Rags occasionally, because I love the score. I think there is a really good story somewhere in that original musical, which was criticized for being too ambitious, i.e., trying to tell too many stories. It'll never happen, but I can dream.
