I love day and night cycle, but it's really up to Larian if they have enough time and resources to add this aspect in the game. I feel like it could open up a can of worms if the settlements act the same way during the day as during the night, so they need to make different routine. It's not easy and potentially adding bugs. With that being said, if it's added, it would be nice, but if not, then I would understand since it's not something that could implement over night.
Since this isn't a sprawling sandbox, no complex routines are really required. The linear nature of the game would remain. This would only need to affect enough encounters here and there to give the illusion of passing time. Scripted encounters would only have different lighting (unless Underdark), which opens up for more varied tactics. The regular encounters affected wouldn't need change beyond adding campfires and sleeping enemies (add as needed for balance). Animations for going to sleep, some appropriate voice acting (yawning etc.).
What we would get in return for not that much work would be three very important things; improved immersion, improved balance and narrative consistency/coherence. The ever important immersion of a world where time is not frozen. A framework for the resting mechanic that would address serious balance issues (D&D classes are balanced around resting a certain amount where resting is infinite in BG3 currently). We would eliminate the *huge* narrative dissonance (story telling us we're running out of time, but have in reality all the time in the world...and then some).
Larian indubitably has a system regarding the Tadpole power and how it affects the player over time. More use, embracing the change, would likely lead to more power in the present, but more negative outcome towards the end. Without it being as bad as to override player agency, locking the player into catastrophic failure/"worst" ending. Wasting a lot of time on sleeping could contribute to this system of empowering/accelerating the change. Players sleeping excessively could be given hints/warnings of this having unforeseen consequences at a later date, indeed such a conversation is already in game and there are scenes that describe the ongoing changes.
I firmly believe the game would benefit enormously for the resources needed for such a change.
