The special episode may feature a number of previous actors reprising their respective roles as Doctor Who.
It was somwhat of a tradition in the previous incarnations of the show for former stars to make a reappearance, reprising their roles in episodes in which the Doctor chances to encounter himself, most famously in the classic episodes, The Three Doctors and The Five Doctors, which starred the first three and first five Doctor Who stars respectively.
It leaves us guessing then when we hear (from Blogtor Who via Bleeding Cool) that the 50th Anniversary episode, which airs in the middle of next year (after the current season is over) will be titled The Eleven Doctors and feature all Doctors - past and present.
The original article on the Doctor Who fan blog has since been taken down, so we can't know how certain Blogtor Who is about each of the elements of the story. That being said, title doesn't seem incredibly preposterous. The inclusion of all the actors, however, is unfortunately impossible.
First, three of them are dead. That's a pretty big obstacle to being in a television show. Though they could replace some of the Doctor's regenerations with other actors or CGI, it seems unlikely. The point of an episode like that is more fan-service that good story-line, so if one cannot get the actors, there isn't much point.
Secondly, it's surprising because of Christopher Eccleston. Eccleston left the quirky show on poor terms, publicly upset about his treatment during production, and promising that he would never have anything to do with the show again. The likelihood that Eccleston would change his mind or make an exception seems low.
So, what would it be? My guess is that all eleven doctors will indeed be featured, but more like a documentary or retrospective than an actual episode in which they all return. I would expect that some part of the celebration will include lots of clips and analysis of the history of the show, going all the way back to the early days. The Eleven Doctors would be a perfect name for such an episode. I also won't be surprised if some past Doctors appear somewhere in the special, or even in the final episodes of the current season, but Eccleston is right out, and he's not the only former Doctor who doesn't really want anything to do with the show anymore.
The article also discusses a rumor that current Doctor Who star Matt Smith will be stepping off of the show in next year's holiday special, which will fall between seasons seven and eight of the relaunched series. This runs counter to other statements we have from the showrunners that Smith will remain through that next season at least.
For now, of course, all of this is unconfirmed. Hopefully, we'll hear from the showrunners soon regarding these tales, and how much of it is true.
The second half of the series kicks off in the new year, but in between we'll have a holiday episode which is slated to air on December 25, 2012. The Doctor Who 50th Anniversary special will arrive sometime in 2013, but the series will be on hiatus after that until Fall 2014, when series 8 is scheduled to be split across the new year, similar to this season.