I've never seen anything on tour (since I live in NYC), but I'd imagine that the 'name' thing isn't as big of a deal. So few people get the opportunity to see broadway shows, that I think they are (somewhat) okay with whomever they get, as long as the perfomrer is suitable for the role.
I saw both Idina and Jackie on Broadway, about 6 months apart (Idina first, in previews). Both were amazing, yet different. Jackie definitely did some different things/riffs with some of those big notes (after my daughter wearing out the soundtrack between the two shows and hearing Idina over and over again) it was a nice variation. I am not at all downplaying Idina- we love her. But she is not as young, fresh and vivacious as she used to be. I get it, I've already 'flirted with 40'

and my schedule is not nearly as demanding as hers, and I am tired jsut thinking about what she has to do. Jackie is much younger, not technically the age of Liz/Beth. But she pulled it off, and well I might add. The audience appeared to be at about 75% (we won the lottery, and entered knowing she was in it). We saw her as Elphaba, and we really wanted to see how she was in this role.
That being said, I do not see Idina stepping in at all. She is in talks to do a show produced by Ellen. And she is always talking about the time she does not spend with her son. I don't think she's about to commit to taking him all over the country, or is willing to split him even more with daddy (but I don't know her, so this is all speculation).
While we're throwing Elphabas around, how about Willemijn? Wouldn't that be interesting