Whoops! Looks like the next piece of downloadable content for Borderlands 2 is called "Tiny Tina's Assault on Dragon Keep."
Borderlands writer Anthony Burch tweeted this picture, which has since been deleted (but not before the folks at Stealthy Box got a screengrab). There in the background is a poster that sure looks like the next piece of BL2 DLC, which developer Gearbox has said will be out in late June.
When contacted by Kotaku, Gearbox declined to comment. At PAX East in March, the company showed the character Tiny Tina teasing something—presumably this new DLC.