Update is out next Thursday.
They added act 4.
They're removing the cruel difficulty (previously you had to run through acts 1-3 twice consecutively, now you run 1-4 + 3 small "interlude acts" that serve as fodder to level you up)
They added new tiers to support gems and removed the restriction that stopped you from having multiple of the same type supporting different skills.
They added a new auction house system that allows trading buying items from other players with no need for them to accept the trade, so if an item is listed on the trade site you may always buy it instantly.
There's a lot of balance changes and additions to the crafting system, too. It's looking like a biiiiig patch.
time to line up for the slop!
Didn't even mention the new Abyss mechanic. It seems like they wanted to have a mechanic that looks, superficially, very similar to the old PoE1 Abyss mechanic, but with a new twist. Instead of simply adding monsters to areas, it will consume existing monsters and league mechanics in your map as you complete them, and make them reappear as stronger versions with new unique loot. There's new Abyss essences, support gems, socketables, uniques, and more, with the general idea that adding an abyss to a map that already has special content in it will enhance the special content with Abyss rewards.