Renee would be wonderful, but this role would be an absolute waste of her gifts (she would make an excellent Madeline, though.)
Box Office Wise, they'd need someone who is a real, outside-of-broadway name for Viola. It's built for stunt casting - minimal dialogue, maximum attitude, almost entirely sung through. But I'll also say, having seen the show both with and without Michelle, I'll say she really does sell what she's given. This girl can REALLY sing, and that is no small feat in this role. Her vocal placement, her ability to just land those runs cleanly and effortlessly, that insane ping in her tone...that's not something everyone can do. Ximone Rose is great as Viola (and yes, sells the dialogue more convincingly), but she doesn't sing the role half as well, and dang it that's worth something! I remember, at intermission, saying to my date "I feel really bad about all the jokes I've made about Michelle Williams." I then proceeded to spend the next several months making more jokes about Michelle Williams, but that's not the point! The point is...Viola's going to be harder to recast than people think. All four of these roles are.