Last thing we heard Borderlands 3 was not yet in production with Gearbox focusing on other projects (like Battleborn). But that changed, during the Borderlands panel at PAX South, where Gearbox boss Randy Pitchford confirmed the company was "ready to start" production on a new game in the franchise. Which most potentially means: Borderlands 3 is on.
Yesterday Pitchford wrote a tweet in which he wrote: "We want to meet great artists, designers, coders, producers and other developers to help with next Borderlands!". It would appear that there is some ways to go until we can play it, but hopefully in the 2-3 years. In the meantime there's The Handsome Collection and Tales from the Borderlands to engage in.