I think when you are developing a show (and I'm assuming a musical) the number of "divas" is dwindling, so you have to figure who you're writing for from who is left, do you write to both divas strengths and is there enough material to split between them, all assuming the divas stick with the project through to opening night? And you have to assume what you write will actually work. Take a look at War Paint, which had a good score but a book that was hampered by a "this happened to her, something similar happened to her..." over and over again. And when you write for a diva and they have to replace a hip, a la War Paint, there goes whatever advance you might have and you have to close early. I think writing or producing for more than one just has too many landmines for modern Broadway.
"Hey little girls, look at all the men in shiny shirts and no wives!" - Jackie Hoffman, Xanadu, 19 Feb 2008