Good sales means more RPG fodder in the future and maybe a D:OS3.
I wouldn't say that good sales [of BG3] means maybe a D:OS3. If anything, relatively disappointing sales of BG3 would be more likely to give us a DOS3, as Larian would decide that making D&D games isn't profitable and go back to their golden goose. Assuming of course that sales of BG3 are good enough that Larian doesn't go bankrupt, which is already true I think.
Whereas if BG3 sells 10M+ copies, then I doubt we'll see another DOS game for a while.
...or Larian goes BIG and starts production of BG4 and D:OS3 at the same time.
Would be interesting because of engine synergies.
Can you imagine what Divinty Engine 5.0 will be like?
Also there would be another interesting RPG IP... Lord British, the Avatar, the virtues... starting in the ruins of Skara Brae, I bet Ultima X would be absolutely amazing when done by Larian.
