There's rumours that at one point they're going to be doing an episode of Dr. Who which features every single Doctor ever (or rather, accurate representations of them). Cameos of some older doctors have been appearing all over the place this series, and what could POSSIBLY be a more dramatic point to place every single doctor ever?
The explosion of the TARDIS, every single major Dr. Who enemy ever converging on one place and time, pieces of space and time that should never exist crashing together and the ensuing cracks deleting people from the time-line and a VERY high River Song density, as well as the frequent referrals to the most feared man in the universe?
If the Ood appear again I'm gunna fucking kill someone. Same with Rose, Torchwood and Donna. They should really keep a lid on that now that 10 is dead.