We may be deep into Season 2, but Blizzard is already sharing some tiny details about its broad goals for Season 3, as well as a few specifics.
One of Season 2's bigger additions is the Blood Harvest event. Blood Harvest is a recurring in-game event that covers a certain portion of the map. It ties into the season's theme of vampirism and its effects on Sanctuary, but it's effectively also a version of the existing Helltide event.
Unlike Helltide, however, Blood Harvest zones are much more densely-populated, and the event itself is always available. Both of those factors have been especially well received by players. It follows, then, that Blizzard will be using that feedback to make Helltides better.
As revealed on the most recent Diablo 4 Campfire Chat, Season 3's Helltides will be up for 55 minutes every hour, which will make it easier to farm Forgotten Souls (and all other sorts of Helltide drops).
Blizzard also reiterated during the stream that itemisation remains the highest priority for the developer, followed by endgame content. Though no specifics were shared, it sounds like Season 3 will bring about Diablo 4's biggest tweak to loot, affixes, power and distribution.
In the more immediate future, players who wrapped up the Seasonal Journey for Season of Blood have the Abattoir of Zir dungeon to play, starting December 5. A week later, on December 12, Diablo 4's Midwinter Blight holiday event will kick off. It will be live until January 2.