Yeah I don't want every actor playing the Doctor to feel pressure to leave after exactly three/four years, there's no reason that they can't stick around a bit longer and further develop the character, especially as Capaldi is going to have almost a year's break now before they start filming series 10

I have a nasty suspicion that he probably will leave with Moffat though, it seems to be the done thing for the new showrunner to start off with a fresh slate :(