There seemed to be cause for concern over Brothers in Arms: Furious 4 due to trademarks, but that ended up having to do with Ubisoft and Gearbox Software filing jointly, an issue which is now being addressed. There's still the question of why we haven't heard much of anything about the project.
Speaking to CVG, Gearbox CEO Randy Pitchford stated that "the game has evolved, I think people are going to be surprised by what they'll see, and it's still evolving. One of the reasons why we're not talking about it now is that it's evolving and we need to make further changes before we can start talking about it."
Not entirely surprising to hear. Pitchford was thoughtful enough to say when we might get more information on Furious 4: possibly "between the releases of Borderlands 2 and Aliens: Colonial Marines, but certainly I won't [talk] before the release of Borderlands 2. Those titles release in September and February, respectively.