Not a solid release date, but I'm willing to bet on 9/14, 9/21 or 9/28 if 2K and Gearbox want to keep their September time frame originally mentioned. It is, as you've most likely glanced already, a set of new screens and posters for the DLC. Nothing too revealing, but something to make you look at and give a thought about dropping the $9.99 for the DLC. Or at least something to print out and post on your desk at work to get funny looks.
Nothing makes me eyeball new DLC like Fidel Castro Claptrap hybrid poster to promote our robot overlords. I'm serious here.