As soon as the BBC decide to opt out of the fight for The Voice, it was clear Doctor Who would move to Spring 2017.
BBC One doesn't NEED Doctor Who in Autumn/Winter - it has it's biggest ratings banker - Strictly. Having Who and Strictly is a strong lineup but, particularly when Strictly is airing longer episodes causes scheduling difficulties - Who fans moaning Who is on too late, ITV moaning that Strictly clashes with X Factor, Usual suspect politicians and newspapers moaning because they can...
The Voice going means BBC don't have any ratings banker in the Spring, well unless Demot's Total Wipeout with cars programme does a lot better than I think it will.
So BBC move Who - which hasn't been regularly on in autumn anyway, to Spring. Stops rating going from boom pre-christmas to nothing after. Means they can schedule shows they hope will be hits in the future around Strictly AND Who, to try to get them some inhereted audience.
It really is as simple as that.