I get the feeling that the Christmas special is going to be 1 part of a 2 parter that'll resolve in the first episode of season 8. I don't know what it is particularly, but it feels like a combination of things. The trailer just feels very, "Stolen Earthy" to me, if you get what I mean.
I wouldn't be surprised if the special ends with 11 starting to regenerate and then season 8 ep 1 resolves the story.
The doctor's "permadeath" feels like it should be a bigger narrative event then just a one 90 minute episode.