In a recent interview with NowGamer.com Gearbox CEO Randy Pitchford alluded to even more content for the 4 player shoot-and-loot Borderlands franchise. Whether or not the new content is even more DLC or a proper sequel remains to be determined. In the interview, Pitchford acknowledges that the Borderlands team originally planned for the The Secret Armory of General Knoxx to be the last piece of DLC, which was then followed up by last September's Claptrap's New Robot Revolution.
I asked the same question after the fourth (DLC) and the answer was 'Well, it's the last one we've planned.' We were really excited to do more and the customers were really excited about more: We love what we've done with Borderlands and we know that there's more that we need to do and that the customers are looking forward to. We know we're not done with the franchise and we'll be letting you know what we're doing before too long.
Gearbox has been very busy, retrieving Duke Nukem Forever from development hell while still working on Aliens: Colonial Marines. After four DLC's and and Game of the Year Edition, fans of the series could potentially have spent well over $100 dollars on a game that was not expected to be such a smash hit. Sequel or no sequel, as long as there is new content, bigger guns, and badder enemies, they'll get my money, even if it's $10 bucks at a time.