Art Director Scott Kester pointed out that if Gearbox didn’t make Battleborn a few years ago then Borderlands 3 wouldn’t be as good now.
He also said the DLCs will be as meaty and substantial as they’ve been for previous Borderlands games.
Source: N4G PC Gearbox: If We Didn't Make Battleborn Then Borderlands 3 Wouldn't Be as Good; DLC Will Be Meaty