The Crown Tundra and what we know so far
Peony has a daughter
Hidden ability capsules exist
The Tundra is bigger than the Isle of Armor
There will be a new tournament mode of 2 on 2 battles where you team with an Ai to go up against other opponents.
Sonya has a waiting plotline there
4 player online mode where you explore dens to search for legendary pokemon
There are 2 horse like pokemon yet to be revealed

That's what we know so far, what's rumored is
Mega evolution may return
You will be able to battle past champions from the previous gens
You will be able to wear the clothing of the previous gen's protagonists
There will be at least one more galarian line introduced
Release November 30th
Your pokemon will be able to walk around the tundra the same way they walk around the isle of armor

if the tundra is as big as they say I sure hope ride pokemon are back, the bike is slow