In the run up to Series 8, Steven Moffat said a number of times that while the two previous incarnations of the Doctor had been great, he felt that it was time to make a change and have a Doctor who was a bit grumpier and snarlier (if that is even a word). By and large this is what fans got last year, and some sections of fandom loved it while others didn't (so.... exactly the same thing that happens every time the Doctor changes, then!). Recently in interviews Steven Moffat has made a few comments about the Doctor's character tempering a bit in Series 9. He basically said that the Twelfth Doctor's going to be funnier in Series 9 which, in part, can be seen as perfectly in line with what Mr Moffat has said all along - that the show, and specifically the Doctor, need to constantly change in order to stay fresh and interesting. It also, however, contains just a hint of back-peddling away from his previous "the old beast needs to snarl a bit" comments. Given that the spiky relationship between the Twelfth Doctor and Clara was consistently one of the highlights of Series 8, this would be a huge mistake.