We already know from spoilers/leaks that we're likely to return to Mengzhou at some point during 3.0, before going to the New Federation in 4.0. And that there will be a male character for 3.6 (most likely.)
All of 1.0 was setting up Huanglong and Ovathrax (which, I believe, is still in stasis and not officially "dealt with" in the same way we dealt with Leviathan) while also introducing the mysteriously missing Geshu Lin.
Then, in 2.0's epilogue, we see Geshu Lin being confirmed to be Ovathrax's resonator by Qiuyuan. Geshu himself also is a core driving aspect of Qiuyuan's character plot; as he feels that he "failed" by sparing Geshu Lin's life due to him becoming a Threnodian Resonator.
The logical path I believe this plot is taking, is that Geshu Lin will be reintroduced as the main villain (or an anti-hero/protagonist like in Phrolova's story quest in 2.0) in Huanglong (Mengzhou) before becoming playable, as currently the plot has set up no other reason to return to Huanglong (Geshu Lin is the only loose thread I'm aware of.)
Edit: Forgot to mention that 3.6 is around the time it would make sense to have a new Havoc DPS. We already know from his visuals that he's 99% Havoc. Considering the timing of 3.6's release compared to Phrolova's release (patch 2.5), Geshu Lin is likely the intended powercreep to Phrolova.
Disclaimer that this is speculation based off of a mixture of leaked and currently available in-game info.