Scape Scape:
As long as the story is good people can forgive past transgressions but a lot of people have moved on. It's now or never.
I didn't hate the last Doctor. I liked some of the 'history' that they explored, like the reason Time Lords only get 10 regenerations, but The Doctor is unlimited. And that the Doctor can't remember this, because their memory of their past is stored in an archive.
But the reason they regenerate at all was to explain how a different actor could take over the role. That brings new life to the role, and gives it a certain feel, based on the actor. Most actors, including David Tennant leave when they feel they are becoming typecast in the role.
I really enjoyed him in the role, but it was time he moved on from it when he did. He was the actor playing The Doctor for the longest. There is nothing in the canon that says a Time Lord can't regenerate into a previous form, but do they really want to?