Locales in the US and American assistants is great, but the Doctor is quintessentially British. I'm not sure how popular an American Doctor would go down as in the States anyway?
Fair point on the actor
One thing I would love to see is have them bring a writer or two of note from the outside to pen a an upside for tther series. For example, Id love to to see William Gibson , the man who gave us Necromancer do a VR themed episode of Dr Who or maybe a Cyberman episode . That could be fun.