A video showcasing a pretty convincing update trailer was leaked to Youtube tonight. It was almost immediately made private, but some people downloaded it and mirrors are now up:
This reinforces a number of other hints that have been dropped over the years, the most notable being a Robotic Bogaloo-style medley of space-themed hats and weapons, anumber of other hints added to the Steaam Workshop, including the contest-winning map koth_probed and pd_watergate, which introduces an entirely new game mode.
Now of course, this is all hearsay and rumor. We might just be getting a well-hyped Community Update. At the very least, TF2 Invasion will finally refer to something other than that failed pre-release design concept that inspired the Proof of Purchase.