This will definitely kill any risky musical film projects. No question. Even with stellar casts or star directors.
Not that ALL musical films (or all films) aren't risky projects, but unless the musical has some sort of built-in wide awareness other than its stars, forget it.
It better be a subject matter that everyone is familiar with. Not just film buffs or Broadway aficionados. It's not enough.
Still very possible not to get canned and actually get made:
Les Miz
Jersey Boys (although with one too many retro music "bio pics" out there, it won't be made anytime soon)
Wicked - no doubt about it
Rock of Ages (would have similar appeal as Mamma Mia)
Forget it:
Ragtime
Grey Gardens
Anything Sondheim including Follies.
Maybe:
Big River - (can be done relatively cheaply, and it's Huck Finn, an American icon)
I also think that In the Heights will tank. Nobody in the general movie-going audience knows what it is. It will have zero appeal to mid-America, too.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22