Back in May, Creative Assembly showed off the Total War: Warhammer 3 roadmap. First on the list of DLC additions was Shadows of Change, scheduled for summer 2023, bringing new legendary lords and units to Tzeentch, Cathay, and Kislev. The Cathayan lord has now been confirmed as Yuan Bo, the Jade Dragon, via a short story CA is giving away. To read it you'll need to login to your Total War dashboard, and if you have trouble with that try doing it in incognito mode, which worked for me.
Yuan Bo (Yuan pronounced kind of like Ywen, rhymes with Gwen, and Bo pronounced like the first syllable of "Boris") is the regent of Central Cathay, who presents himself as a simple bureaucrat. However, like his siblings he's able to transform into a literal dragon, and serves as Cathay's executioner as well as its administrator, so he's not to be underestimated. The short story also introduces the Onyx Crowmen, his flying assassins, which will presumably be a unit in the Jade Dragon's army.
Given that the DLC is called Shadows of Change, the Tzeentchian legendary lord it adds was always going to be The Changeling, a shapeshifting trickster. We still don't know who will be added to the Kislevite roster, though. Current guesses favor Mother Ostankya, a hag mother who is basically Baba Yaga.
Accompanying the DLC will be patch 4.0, adding a free legendary hero and bringing achievements to the Immortal Empires campaign. A recent blog post explained that Immortal Empires will also be getting tutorialization, with a string of missions to guide players through the early turns, and more landmark buildings are being added across the map. In addition, a new slider will be added to the battle difficulty settings to let players control the AI's stat boosts.