They had nothing to show at Blizzcon, because they literally had nothing to show. Really early stage of development. Nothing is set in stone, no systems, no art, they don't even know how they are going to do the new stat squish properly yet. The Maw zone is still up in the air and might not even happen; imagine full sized zone, but nothing to do just like on Timeless Isle.
Allegedly early 2021, but from I heard/understand, we shouldn't expect it until late 2021.