That's not the problem (and in fact, they are adding a TON of new assets, hundreds if not thousands of new models and animations and textures, not just reusing stuff from D:OS1). The problem is giving a sufficient number of NPCs reactive behavior to the day night cycle to make it actually immersive, instead of just pretty. You seriously underestimate the amount of work it takes to give lots of NPCs schedules, new quests, etc. They could do a minimal amount of scheduling, making vendors go inside, 3-5 night-specific quests, etc. but I think Swen would much prefer to go all the way. It's just like with the origins, which aren't going to be little gimmicks but have a massive effect on the game. Trying to throw a well-developed day/night cycle on top of that is asking too much.
OK...development of the game is just beginning...what's stopping Sven from "going all the way", exactly? It seems silly to reject a concept which you have never attempted to implement and for which, therefore, you have no concrete notions as to what it would consume in terms of developmental resources. This is kind of a chicken-egg scenario, imo. If you haven't ever done a night cycle, how can you reject doing it on the grounds it will consume resources you do not have? That's an illogical premise because since you have never attempted it in a game you cannot know what it will cost to implement.
Except they did try to implement in their first game, but they saw how much work it would be. Maybe they tried it with a few NPCs, had a lot of problems, saw how much time that took, and can extrapolate from there that they didn't have the time or money to do add it. I made a mod (unfinished) and saw how hard it'd be to make a good day/night schedule, so I imagine Larian could see it even more.
Permanent daytime is less immersive than a slightly incomplete day/night cycle, yes, but the point is Larian doesn't want to half-ass it. How hard is making all the businesses close and people go to sleep without breaking a bunch of quest behavior and then adding enough for players to do at night (instead of wow, everyone's asleep so I can't complete these quests) -- it's hard, especially in the Divinity Engine. And if the player needs to sleep, that'd be a lot of work for something players wouldn't even see. It's just another layer of complication on top of what is building up to be an extremely multi-faceted game.
Say you arrive at the town in the demo, and it's night. Is that dwarf still going to bomb that cart? If he does, you have to change some code with a bunch of people gone. If he doesn't, another complicated thing to code for, and the player will be missing a big set up for a lot of tension in the town. Now imagine doing that with nearly ever event, only making some of them night-only. People's behavior does and should change with the day-night cycle.
Larian could've done the day/night cycle if they sacrificed some other aspect of the game, like the origins. They should learn to properly craft a multi-faceted narrative before they spend a lot of money on something that is mostly aesthetic and just doesn't quite move the genre forward as much as something like hugely impactful origin stories and competitive questing. I haven't played Witcher 3 yet, but that's a game, like Skyrim, that has a huge focus on immersion. It also, I hear, has great quests, good combat, and other things. But they also had a lot more money. And, it's their third game in the series. Witcher 2 had a cycle if I recall, but I don't remember it impacting the game all that much. And I don't know how much it impacts Witcher 3 either.
