I just read this thing on Den of Geek, where they suggest ten possible actors who could play the Doctor -- one of the suggestions is Sam Rockwell... I think that if the Doctor had to be American, it should be him.As long as the film isn't funded out of the licence fee, I see no problem. However, I doubt that the film would be commercially viable with anything less than a large budget for SFX, and, even then, they're going to need expensive, big-name casting to attract punters in the markets other than the UK. So, be prepared to see someone like Johnny Depp in the lead role - actually, I don't mind that notion as much as some do.
Doubt it's going to happen, though. Yates has said they want the movie to have a "British sensibility".