Whether hes a good man or not, we know that hes got one of those faces. By which we mean, weve seen him before and hes now acknowledged that. Yes, Moffat has elected to make it a story point that the 12th Doctors face has appeared in Doctor Who before. Its a given that television shows will reuse actors, but in this case its front and centre in the narrative. More than that, the Doctor has made it so:
It's funny, because, I'm sure that I have. You know I never know where they come from, the faces. They just pop up, zap, faces like this one Why this one. Why did I choose this face. It's like I'm trying to tell myself something. Like Im trying to make a point. But what is so important I can't just tell myself what I'm thinking?
Its an old face, for an old man, in a season obsessed with giving us callbacks to previous storylines and older episodes. What can this mean?