I want to have a discussion about the impacts of the special. Obviously there will be SPOILERS.
As anyone who watched the special knows, there were several bombshells dropped during the special. First and foremost is that the thirteen incarnations of the Doctor were able to successfully trap Gallifrey in another universe, preventing it's destruction. This is a complete retcon from the history established by the introduction of the 9th Doctor in the 2005 reboot. This change is both a brilliant stroke by Moffat and also slightly problematic.
On the brilliant side, the preservation of Gallifrey opens up a myriad of storytelling possibilities for the Doctor Who team. When Peter Capaldi is introduced in the Christmas Special, his journey as the Doctor will have a clear direction: find Gallifrey. This quest can take over the entire 8th Series or Moffat and crew can piece it out over multiple years. Either choice has merit, but if they wrap up the story at the end of Capaldi's first year, they gain another potential story point: MORE TIME LORDS!
When Christopher Eccleston was introduced in the episode "Rose", we learned that he was the last of his race, the rest having been lost in The Time War. While that creative decision worked for the show at the time, the lack of other Time Lords was limiting. The Doctor's Time Lord enemy, The Master was eventually reintroduced in the three-part ending to Series 3. More Time Lords, including Rassilon, were reintroduced in the two-part episode "The End of Time." In each of these appearances, the other Time Lords are enemies who must be defeated, a difficult action for the Doctor, since he is once again ensuring he is the last of his race.
New Time Lord characters (or even newly incarnated classic Time Lord characters such as Romana) don't have to be adversaries for the Doctor now. There is no need to preserve him as the last of the species. It would also be an interesting story arc if the Doctor finally finds Gallifrey and is called upon to answer for what he has done over the centuries, including his actions during the Time War. The reintroduction of Gallifrey and the Time Lords can only expand the Doctor Who universe beyond what the setup for Nu-Who has previously allowed. In my opinion, there are a few questions that need to be answered as the show moves forward.
The first question that Moffat needs to answer is the question of regeneration limits. We have now seen thirteen incarnations of the Doctor, including the War Doctor and Capaldi's Doctor. This doesn't even take into account the Valeyard from Classic Who, a character that supposedly existed between the Doctor's 12th and final form, or the appearance of Tom Baker in the special as another future incarnation of the Doctor. The idea of the regeneration limit has run it's course. The show has now made it so muddled that Moffat just needs to hand wave it away. Have Matt Smith say "Timey wimey! I guess thirteen isn't the limit anymore!" and then never speak of it again. Don't say it's twenty now or that River Song gave the Doctor eleven more lives. JUST MAKE IT GO AWAY.
The second and more important question is how the preservation of Gallifrey affects the Doctor as a character. When the Doctor made the decision to destroy his own people along with the Daleks, it changed who he was. The Ninth and subsequent Doctors were burdened by this decision and this burden affected them. The special did a good job of explaining that the War Doctor and the Tenth Doctor would have no memory of this changing, so it would not impact the events that have happened over the course of Nu-Who. The Eleventh and Twelfth Doctors however, will have full knowledge that they didn't destroy their own people, but still have the memories of having done so. I think it is important that the writers of the show not gloss over this new knowledge in the new series. I don't pretend to know how this would affect the Doctor, but maybe it is time for the sadness in his eyes to be replaced with hope. An actor like Peter Capaldi may be just what the series needs to properly depict the conflicting emotions the Doctor should be experiencing.