Absolutely NO role is "uncastable," especially the ones you listed. Some of the most brilliant performances I've seen on stage are by foreign actors - thank god those casting directors don't have the same mindset as you.
Obviously, there is a bartering system between the two equities, but I have no idea what that point has to do with what you're trying to say.
And as far as you thinking that the ONLY reason she did FIDDLER was so she could come back as Poppins is baffling. Is it a rule that if a foreign actor wants to have a lead role on Broadway, you must first have a supporting role? Come on, that's rediculous. She wasn't even cast as POPPINS until well into her run in FIDDLER, then she had to break her contract to get out of the show.
I'm not saying she's the ONLY one to do this part and that some other actresses (American or not) couldn't do a better job - I'm sure there's SOMEONE out there that could. I just don't understand your logic behind NOT wanting a british actress to do the part. Besides, POPPINS is a purely British musical - a British cast would make it that much more authentic. Do you feel the same way about Nathan Lane originating his role in THE PRODUCERS in NY, then originating it in London? Or what about Adam Pascal originating RENT on Broadway and in London? Surely there were some british actors who could have done them just as well, why send american actors over there?
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson
