1. They're working on an entirely new IP. Likely not a medieval fantasy game
2. They're working on another licensed sequel to a beloved rpg. Something like Arcanum or Vampire the Masquerade
3. Swen somehow managed to convince EA to sell him the Ultima IP and got Richard Garriott to license him Lord British.
Never played Arcanum but just taking a quick glance it on Steam it looks like a perfect fit for Larian. "Magic and Technology coexisting in uneasy balance"
Personally I dislike the "tech" that appeared in both DOS2 and BG3 but I could see Larian having a lot of fun with a concept like that.
I thought the House of Healing had way too much of a Victorian era feel to it, maybe some kind of steampunk horror setting will appeal to them.
