I want a day/night cycle as part of a system that coherently represents the passage of time.
Right now, it becomes night whenever you feel like taking a long rest, which could be two minutes or 50 hours after you've woken up. You are able to sleep away the majority of the day or stay awake for days on end with no repercussions. There's no verisimilitude there. It would be nice if resting made some sense - "as much as you want, whenever you want" is lazy design and boring (not to mention unbalancing).
Larian doesn't really do veris..verymilishtattude, doesn't do immerchion, as long as it perceivably intervenes with the most cheesy perception of fun.
You can for instance camp the merchant selling invisibility potion, pickpocket, and rest. Rinse and repeat 100 times. Pickpocket is a brokenly overpowered legalized exploit and blatant screw you to even the slightest hint of risk vs reward mechanism. It allows players who don't care to roleplay (or that roleplay kleptomaniacs), to break the economy totally. One might argue people who don't want that kind of cheese/roleplay a moral character, can ignore it - but you get punished for having scruples since you're less likely to afford the ready supply of (in practice) free stuff from merchants/NPCs. The unlimited rest/eternal day comes with its own set of issues; balancing, immersion and narrative dissonance.
And night vs. day doesn't have to be a cosmetic thing at all. How about having the behavior of NPCs and other creatures change over the course of the day? Want to rob a shop? Go for the brash smash 'n grab in full daylight or try to sneak your way in when people go to sleep at night. Looking for a trophy from some rare animal? Fight it when it's alert and hunting at night or try to sneak into its lair while it sleeps through the day. Ambush the goblins late at night, when most of them have passed out from drinking, but knowing that your humans without darkvision won't be able to see as well.
Realistically it DOES have to be somewhat cosmetic though. Larian has explained their lack of a day/night cycle on the grounds that implementing one would be a humongous endeavor that would constitute a waste of resources for what it gives in return. I tend to agree a Skyrim level of complex AI would be wasteful in a mostly linear game. That said, there are compromises that are good enough to provide the illusion of passing time. NPCs can react to time while still being mostly frozen in space. Add some campfires and sleeping foes depending on diurnal/nocturnal behaviour. Add extra sleeping enemies to balance encounters as needed. This wouldn't have to effect every encounter/every NPC, just enough to provide us with the cosmetic illusion.
In addition to somewhat remedying the many glaring issues with the current lackluster implementation, we would open up for more diverse environments and more varied tactics and combat. Well worth it in my opinion.
