I don't know why opera and plays can't get original ideas any more than they do, which is rarely.
Yep, most big musicals these days are based on successful movies: The Producers, Hairspray, Dirty Rotten Scoundrels, Spamalot, Momma Mia, etc. And that's not even counting the ones based on Disney movie versions of classic tales: Beauty and the Beast, The Lion King, Tarzan, Mary Poppins, etc.
I would like to see the musical Gray Gardens, based on the bizarre Maysles Brothers documentary about Jackie Kennedy's reclusive relatives Big and Little Edie Bouvier Beale.