Mary Testa would be perfection, yet for whatever reason she would not be given the role, I think. People seem to keep casting her in these tiny roles when she is probably one of the best NY actresses of her generation.
I've heard Ebersole's rendition of "Everything's Coming Up Roses" and it's dreadful. It's just not her role. She would be quite miscast, her voice is not up to it, and her persona doesn't fit Rose (and seeing her TRY to be Margo Channing sort of proved it to me).
The few actresses that are perfect for Rose at this point are too big to take any kind of replacement role at this point. Donna Murphy would be ideal but she deserves her own production, and not yet, as LuPone says she is just at the age where she feels she knows how to handle Rose from a technical aspect, so Murphy needs about a decade more before getting there.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"
