After repeatedly trying to get an answer, we now finally have it confirmed that Aspyr Media will be doing no further updates to Borderlands 2. While Aspyr Media are still continuing to update their ports of Civilization VI for Linux / macOS, the situation with the Borderlands series is just sad.
You might be confused, since Borderlands 2 is from 2012. So why are we mentioning this now? Well, it came to Linux later in 2014 and last year it gained one final DLC with Borderlands 2: Commander Lilith & the Fight for Sanctuary plus the Borderlands 2 Ultra HD Texture Pack. Both of which are missing for Linux and along with those and updates to support them, this broke cross-platform play between Linux, macOS and Windows.
Aspyr Media said last year they were working to get it all up to date on Linux. Time went on, we reached out to them a few times and each time it went unanswered. Until today that is, where their partners got in touch with us with a statement: "At this time, we can confirm that there are no further updates planned for Borderlands 2 on Linux and Mac. We will continue to provide customer service support to players via support.aspyr.com.".
Note: while it wasn't mentioned, this all likely affects Borderlands: The Pre-Sequel too.
Obviously all games stop being updated at some point, not everything is a live-service style game and developers do move on. Still, missing entire updates and DLC is ridiculous. We have no idea if this is due to Gearbox Software, 2K or Aspyr Media directly and we likely never will as these sorts of deals are never made public.