The extra's that played Dalton Academy students have confirmed through twitter that they were asked to film in one final episode, this being it. It is thus thought that the episode will deal with Kurt transfering to Dalton Academy. It is also thought that this was done to keep the contents of this episode a mystery as based on time they have less then 20 days to film and put the episode together which would prevent many spoilers from leaking.
the tenth episode is the secionals episode
Spoilers tell us that Kurt is still at Dalton Academy and therefore is not part of New Directions numbers. The twelfth member, discovered through a behind the scenes picture is in fact Lauren Zizes.
It is likely that this will be the episode where Dustin Goolsby returns, which means most likely Sunshine Corazon as well, since Cheyenne Jackson, who plays Dustin Goolsby, has confirmed at the 2010 Emery Awards that he had filmed his second appearance on Glee in the same week as the awards, and that filming for this epsiode was done in early November.
then sue the grinch