Possible Spoilers, I suppose. So if the Matt Smith Doctor believed he was the last Doctor, then the Capaldi Doctor was not part of his plan to save Gallifrey in "Day of the Doctor". If the Capaldi Doctor was not necessary, then why was he there? The Capaldi era looks to start with memory problems (like has happened before after regeneration), but what if these memory problems are stretched out a bit. Could it be that the Matt Smith Doctor figured out something else he could have done to save Gallifrey during his time on Trenzalore? The Matt Smith Doctor would have thought he would never have a chance to implement it; but now he can through Capaldi. The problem is that Capaldi doesn't remember. I think it could be fun to see the Capaldi Doctor with a bit of a personality disorder as he slowly remembers each past incarnation of himself. With a 13 episode series, Capaldi could have one episode devoted to an adventure related to each Doctor until he finally makes his way to the Matt Smith revelation in episode 11. Then a two part finale implements the revised plan that brings Capaldi into the resolution of "Day of the Doctor".