Executive Producer Steven Moffat describes the special as "your favorite Christmas movies at once". Will Michael Gambon then be playing Santa Claus? Will the Doctor actually meet Santa Claus? At least we know that all the Christmas carols in the episode will be sung angelically by Ms. Jenkins.
A few more plot details have been released. It will involve a honeymoon, most likely for the newly married couple of Amy and Rory. It seems sort of strange to invite anybody else along on one's honeymoon, much less the Doctor. On the other hand, "the Doctor" and "strange" go hand in hand. Besides which, someone has to drive the vehicle.