Absolutely new specs/hero trees, there’s so much potential there. Like an ACTUAL Shaman themed spec for Shamans where they commune with spirits, weaponize them, fling hexes and curses and potions, etc. Or melee BM and ranged SV, etc etc. there’s so many things asked for that could be added as spec flavor to classes we currently have.
There’s 2 maybe 3 new classes that even really have any unique hooks to bring to WoW, but there’s dozens of sub-specs we could yet add that would add so much more to what we already have and would flesh out classes.