Honestly, we’re talking completely new engine and none of Larian’s built-in stuff with regard to environments and the like that they had from their past divinity game. No one is going to have that just ready to go. So, they need to shop for a dev studio that has a past game that shows what they want.
Obsidian doesn’t have that, maybe the closest being Dungeon Siege 3 or Pillars of Eternity, but those are very basic, not as open, very little environment related and altering capabilities. So, we’re talking a step way back on what Larian delivered. Zero scene experience to line up with what was done in BG3. Okay conversation tree designs, but still needs more complexity.
inXile has Wasteland 3 as a base model engine, and I think that’s better than Pillars of Eternity from Obsidian. But, still needs to be more open world, more environmental effects, and a much heavier rules set adaptation. But, not a bad overall engine as a base, but still a ton of work. Zero scene experience to line up with what was done in BG3. Needs a ton of work on that entirely.
Tactical Adventure did the Solasta game. Really good and more accurate as far as 5e rules than BG3. But, again, if the expectation is similar to what made BG3 a big hit, engine isn’t designed for moving the camera, is a bit outdated in graphics, doesn’t have in-game scene elements, and needs much better writers/voice actors.
Owlcat of pathfinder games is another choice, even though they’ve recently moved on to WH40k licensed games. Again, though, the engine is the biggest issue here to match up, but it’s a much better option overall than Tactical Adventure. Another question is writers/story telling, as much of their overall story telling bits are very limited with a lot of random worldbuilding elements that are just +- of some attributes.
TBH, no matter who takes over, it’s just not going to be like BG3 much like how BG3 isn’t at all like BG1/2. And BG3 was so successful because of how much Larian was able to put in with their engine and how focused they were on players having ridiculous control over the story being told. I just don’t see the next BG being the same and depending on what it is, it might be good but I’m not as big of a reach as BG3. It’s way more likely players are going to go into BG4 (or its spiritual successor if it moves away from Baldur’s Gate and into Neverwinter or something like Plansescape) expecting much of what is in BG3 with more options, new and older characters, and the same level of control over what they’re doing. If it doesn’t have that, regardless of who makes it, it won’t be as successful, IMHO.
