Among the challenges is how to handle Addie. Should she be, as in the film, only a voice? A celebrity voice? e.g., Meryl's? Should she sing? So much of the power of the movie is that we see Addie only in our and the other characters' imaginations... should that be preserved? Could changing that possibly work? Not sure.
Give it a gay twist and have Anderson Cooper do the voiceover, just like he did in the recent H2S revival.
Honestly, I think this is one movie that would make a great musical. Plenty of good female roles, a helluva tight screenplay, a great story, and a rather unfamiliar movie that won't just play because of name recognition. Some movie can make great musicals, unlike the current movie-to-musicals currently plaguing Broadway.
Also hoping to one day see a musical version of A Face In The Crowd. There's a show that unfortunately is timeless.