I'll make here and now what may be a highly controversial prediction. Early in 2019, right around the time that BG3 was first announced, Swen Vincke said in an interview precisly in response to the question of why BG3 instead of D:OS3, something to the effect of: Life is short. I have only so much time to make the games I want to make. I don't want to spending all my years making the same games again and again and want to do something new/different.
In the light of Vincke's remarks in that interview, I doubt there will be a BG4 or even a D:OS3. After BG3, I expect Vincke will want to move on to yet another new IP to create a new game that is NOT D:OS or BG and likely even NOT fantasy.
I expect full credit (and worshipping at my feet) when my prediction comes true.
I would be completely on board with a new IP using what Larian has learned and developed in BG3. Turn-based, 3D explorative, story cinematic, character-driven RPG in a new setting would be very fun. Lots of worldbuilding potential there. I could even live without the turn-based part if Larian so chose.
On the other hand, I think there is more money in WOTC properties, especially with the direction of its popularity due in no small part to the pandemic, Stranger Things, Critical Role, and the widespread availability of programs like Fantasy Grounds and Roll20, along with its historic cultural presence since the 80s. Combining the enthusiastic fanbase Larian developed during the cRPG renaissance with the absolutely rabid DnD fanbase might be a smart call.
Edit: All of this to say Larian has a lot of momentum going into BG3. It is up to them how they want to direct that momentum, but it would be a shame to waste it.
