The latest game leak comes from the U.S Trademark office.

Developer Gearbox (creators of Borderlands) have just laid claim to the name “Borderworlds”which suggests a sequel to Borderlands that will span several planets,though that is just speculation.
Given the much higher than expected success rate of Borderlands this is no surprise.

This is further backed up by Take Two saying Borderlands is a “New Key Franchise”