OK...development of the game is just beginning...what's stopping Sven from "going all the way", exactly?
A tenuous grip on sanity?
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.
They did try it for D:OS 1. It turned out to be a shit-ton more work than was expected and it was too hard to put in.
Yes, they could do a cosmetic-only d/n cycle which changes nothing, and of course that would be much less work. Swen has considered that possibility and rejected it.
Adding in a cosmetic day/night cycle for D:OS 2 sounds like it would be more immersion-breaking than adding one in for D:OS 1, since there are things which will happen "tomorrow", like the Divine Magisters arriving on the island. Since they will never arrive on the island, having people say that they'll arrive tomorrow, ignoring the fact that you could have months of day/night cylcles happening in the meantime wouldn't be any more realistic than eternal day.