Yes, that was my expectation at least. I don't know about others, but I fully expected either a "5E core rule" toggle or gameplay mode. Now I have to rely on mods and either have to learn to mod BG3 myself rather than spend time playing it or I have to trust that someone does a mod that accomplishes what I want.
Getting to 5E core is a bit of a journey, considering we stepped off that path so long ago. I suspect the biggest problem will be balance. Consider what happens once you return ranged weapons to what they used to be in 5E. Eldritch spear should mean 300 feet eldritch blast range. I'm pretty sure that will break just about any encounter in the game, because the AI just can't see that far. But then the AI gets those abilities too, and suddenly encounters might well begin to overlap.
I don't see Larian really changing their map layout approach, which means everything is so ludicrously compressed, which means 5E distances will almost necessarily get really weird. And to fix that, it's going to be necessary to compromise on the rules.
The point is, once we start changing the rules, the logic of encounters changes, and trying to fully grasp what each change does to each encounter across the game is sufficiently enormous that I can understand why Larian don't care much to support multiple different sets of rules. I imagine this would also be an enormous problem for a modder.
