I wrote Gearbox and this is what they told me-
Hey Vault Hunter,
At launch the Stadia version of the game will reflect all updates and fixes that were released through October 24. Noteworthy features coming soon to the Stadia version of Borderlands 3, expected in early 2020, include endgame content like the Takedown at the Maliwan Blacksite and Mayhem 4 difficulty, dedicated loot pools for bosses, and additional bank space. The first Borderlands 3 campaign add-on, Moxxi's Heist of the Handsome Jackpot, is also expected to launch on Stadia in early 2020.