It is possible that Matt Smith will depart the role of the Doctor after the 50th Anniversary, if that is the case to you end the 50th Anniversary episode with a Regeneration?
After all the next episode up no doubt would be the Christmas special a few weeks later (assuming the episode actually airs on Saturday the 23rd November) and if I were the BBC One Controller, I couldn't resist doing so)
I'm also expecting BBC Three to do something as well in the weeks leading up to and/or the weekend of the 50th Anniversary. Maybe showing a serial/episode from each of the other Doctor's. As well as some sort of documentary on the show to be commisioned. With a theme night maybe on BBC Two.