I also can't see Benanti going into this production. Eliza Doolittle is probably behind her at this point. (And though it would be many years away, while we're talking about her "future," I'm sharing the excitement of many others on here to see her and Kelli O'Hara in a Follies revival.)
As for Ambrose, this is quite an auspicious moment. Like JIMG3 said, though, tonight is only Preview #3, so there's a lot still in store—but exciting times indeed.