Based off of a PAX West conference, it's likely that we're going to be seeing a brand new addition to the Borderlands series. Randy Pitchford, the CEO of Gearbox, said that roughly 90 percent of the Gearbox production staff is currently "working on the thing I think most of you guys want us to be working on." Odds are, that "thing" is Borderlands.
Last year, Pitchford announced that a new Borderlands game was in development, but he didn't come out and directly say that it was a Borderlands title. It might be something completely different, but taking the companies past into consideration, Borderlands seems to be their hottest commodity.
Hopefully Gearbox pulls through with another amazing Borderlands title. It wont be available until fiscal 2019, which would be April 2018 through Match 2019. Honestly, that's not too far away. Granted it isn't going to necessarily be released in April of next year, especially without an official announcement yet, but hey, let's just hope that we get it as soon as possible.