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.
