Assuming there is a sequel, of course. But based on Borderlands' strong sales as a new IP and prior comments to come out of both Gearbox Software and Take-Two, it's more a question of "when," not "if" in regards to a follow-up.
Thanks to the ever-vigilant work of superannuation, a trademark filed by Gearbox for "Borderworlds" has been found. With Borderlands being the fine game that it is and only needing a few crucial additions to see its distinct style of play perfected, a sequel sure would be fantastic.
While I'm personally not a huge fan of the name "Borderworlds," I'd be glad to suck it up and deal with the title if it meant getting a sequel to one of my favorite games of this year. Perhaps the more I hear it, the more I'll get used to it? Things tend to work out that way.
We've asked Gearbox for a comment, but I wouldn't hold your breath. It's seems too early for anything substantial to be discussed on the record.