I agree PF Kingmaker is the king of these toggles (one of the most requested one i remember was the encumbered matters or not in movement toggle), and as far as i heard Solasta also plans to take a similar route, they just gave some hints in their new update. I also really liked what Pillars 2 did with Magran's fires, some of those toggleable options gave the player to chance to tweak certain rules around resting (especially how often spells and actions are refilled), tweaked food mechanic and added food spoiling, whether downed characters permanently died after some turns spent downed or not, added equipment durability, degradation and repair, added timed quests where story reasons backed it up, weather tweaks, special resistances for monsters, hidden enemy stats without identification etc. all of these additions were really clever and they really helped to customize my playthroughs and i think most of these would be beneficiary for BG3 as well to have a toggle for. Given i also intend to play this game multiple times as it looks really cool (and i would like to try out more races, classes) i would prefer to have some options to alter the core gameplay mechanics a little bit every time i do. I know there are mods coming but its just not the same, sometimes mods tend not to be updated every time with the game and usually they also have glitches and clashes with official content (i like mods, there were some magnificent mods made for DOS2, but i prefer to have the option to officially customize the core gameplay with little tweaks for my first playthroughs).
