I don't think casting an unknown is a mistake--tourists will see the show because it's Funny Girl, stunt casting or not and it will get a lot of hype because it's Funny Girl--if they cast an incredible unknown actress, between the publicity the show will already receive and the draw a revival of a popular musical has, the unknown may well become a "known"--that's how Julie Andrews did it.
Personally, I think Lea Michele is talented but they could do better.
