When it was revealed at the end of last season that Dr Saunders is a doll I rolled my eyes (what was that, the third time they used that twist) and decided I wouldn't be surprised if absolutely everyone in the show was a doll. So flipping personalities wouldn't be a problem, more of a letdown.
I'm interested to see how neatly they can explain away the Rossum head's identity though. I still have faith in Joss.