I like the Icewind Dale setting, but, and I’ve said this before, Planescape! That would perfectly match Larian’s sensibility and design philosophy.
This. Unfortunately the Planescape setting is utterly dead but letting Larian have a go at it has the potential to be brilliant. They can do things as dark as they like and still have all the room in the world for wacky fun. The only real problem, aside from getting permission from WOTC, is creating a protagonist that doesn't feel like a letdown after TNO and thematic music that doesn't suffer when compared with the nostalgia factor of PST music. And NPCs that can stand up to Morte and Dakkon.
I think the setting have been largely forgotten by WotC isn’t too big a deal. Larian have said that WotC gave them free reign to do what they wanted, and if they see $$$ signs then they’d be on board.
TNO would be a difficult protagonist to follow, that’s for sure. I think they might need to drop Origin companions and just focus on one dense, narratively complex origin that is flexible enough to still allow multiplayer. That’s a big task.
