i don't know how deep it is now? are we back at level 0 and no deeper? are we keeping dripstone? i saw that we are keeping the new axiotol amphibian. i know we are keeping copper. i don't know how many changes are left before 1.17 is released.
My guess is the Copper, Goats, Raw Ores and a few other things but the World Gen (which they already had working well enough I felt anyways or thought before they added it to snapshots that it would come later) along with the Archaeology and Warden/Sculk blocks will be in part 2.
The 21w15a gives us an idea and I think future ones will continue along with those features, then go with bug fixes just to release something in the next month.
Understandable they are backtracking on world gen (or still working on the other/have more ideas they want to add) as it is a lot of technical changes (like they did in 1.14 with the commands and overhaul of the game in the background) but it seems odd when a good amount of it was already done in snapshots already *shrug*. Either way, we will just have to see what happens.