Right now, the Bloody Harvest event is still underway for Borderlands 3, offering players who have yet been able to get its unique offerings quite some time to get them. Players will have until December 5th to check out this limited-time event, but that's not to say BL3 will be without content then, as it has recently revealed its Takedown at Maliwan's Blacksite DLC. That will drop on November 21, bringing with it new content in the form of a Takedown for endgame players to tackle, which leaves only one thing to be revealed for the start of the roadmap: its first major story DLC.
For those unaware, Borderlands 3 developer Gearbox Software revealed its 2019 Fall/Winter content calendar that include the aforementioned DLCs some time ago. This calendar, of course, kept the deals of the first major story DLC quiet, but it was heavily implied that everything listed here will drop by the end of 2019 (despite Winter technically lasting until March).
Assuming there have been no major snafus to push this back, this means that Borderlands 3 players can reasonably expect the first DLC to drop by the end of the year. Historically, this has always been the case. The first major DLC for the original Borderlands, the Zombie Island of Dr. Ned, released in November followed by Max Moxxi's Under dome riot in late December. Borderlands 2 saw Captain Scarlett and Her Pirate's Booty and Mr. Torgue's Campaign of Carnage drop before the end of the year.
With the addition of major DLC events like Bloody Harvest and permanent add-ons like the Takedown, it makes sense that only one story DLC would drop for Borderlands 3 prior to the end of the year, but with the current release schedule and the fact that it has yet to be announced, this can be narrowed even further.
Chances are, it won't be announced until around the time of Maliwan's Takedown, if not some time later. It also wouldn't likely release prior to the end of Bloody Harvest, which is December 5. Therefore, it stands to reason that this first major Borderlands 3 story DLC would drop between December 5 and 31, perhaps incentivizing holiday purchases of the DLC for those who don't own the season pass.
Of course, with this being the case, there's still no telling what this story DLC will involve. Some things fans and critics have wanted to see is development upon Ava's role in the Borderlands 3 story, more context added to the Calypso Twins, former unseen Vault Hunters like Gaige, Salvador, or Krieg shown in some way, an explanation of the Watcher's Warning in the Pre-Sequel, development upon Sirens like Nyriad mentioned in Borderlands 3, something that shows the connection between FL4k and Zer0, and/or another D&D-style DLC. In other words, there's a lot, but there's truthfully no way to know when and what the first story DLC will cover.
It's even possible that it covers none of the above, though there are a ton of questions fans want answered, and it would be a shame if none were answered until Borderlands 4. Assuming the release falling in December is the case, then hopefully, more info about it will be coming soon.
Borderlands 3 is out now for PC, PS4, and Xbox One, with a Stadia version also in development.