I like to think of it from the developer’s point of view. Borderlands has been a great series that gave a lot more freedom than many games and these developers have been working on Borderlands for a long time now. Borderlands is a game with a lot of freedom but even so the game could be limiting. Battleborn must be a breath of fresh air for the developers. You have a completely new setting with even more freedom, a new graphical style and the ability to design completely wild new play styles.
Compare that do developers that get stuck on a franchise treadmill where every game they make has to be a follow-up to a previous game in the franchise.
If you give Gearbox option A you will have a much happier team that would be refreshed if/when the time to make a Borderlands game comes around again (I say if because they are hiring new blood to work on it, I’m not 100% sure the original team will return to it). Option B leads to burnout and people leaving the company to try something different.
Personally since I’ve been waiting for a new game from Valve for a long time (I’m still not excited about DotA2 or CounterStrike:GO), I’ve had Gearbox keeping me busy for a long time.