If you're poking around the job listings on Treyarch's webpage you might get the feeling that they're working on something new. The following are duties (HA! Get it? Duty?) that point to new games.
Look at the listing for Senior Software Designer: "Treyarch is seeking a Senior Platform Engineer for a position on the team bringing our hugely successful game to a new console." The Senior Lighting Artist asks for someone who "will be able to show good examples of lighting made for games, preferably next generation console."
What are they working on? And what console is it for?