However, we might have a clue, thanks to reports coming in from CVG's "US dev sources," who tell the site that the game is actually Duke Nukem Forever, and will be given a "grand demo" at the show. Rumors have been flying recently about Gearbox signing on to complete the game. Also flying: pigs, in an image tweeted by 3D Realms' George Broussard (who joked with 1UP in a January 2006 interview that he expected DNF to be released "when pigs fly") . 2K did say it planned "something big" at its booth, and this would certainly qualify.
Update: Gearbox creative director Mikey Neumann tweeted a picture of CEO Randy Pitchford wearing a Duke t-shirt. Seems portentous!
Update 2: A partial image from 2KGames' Twitter account also shows the Duke "radioactive" logo.
Update 3: Well, here's the most concrete evidence you could ever ask for. Pikimal [via Shacknews] posted several images, like the photo stand seen above, of Duke Nukem Forever signs at the 2K booth.