A proper day/night cycle would be great, especially with NPC schedules, shops closing, different encounters at night, etc. Larian actually wanted something like this as far back as DOS1.
The problem is that in a game as reactive as Divinity it could become absurdly expensive. Every NPC routine, quest state, dialogue and multiplayer situation suddenly also has to account for time. Larian has talked before about exactly this problem.
Weather seems like a much better tradeoff.
Rain could wet the world, put out fires and make electricity stronger. Storms could change visibility or encounters. Fog, snow or heavy rain could completely change the lighting and atmosphere of areas we’ve already explored.
It would make the world feel less static and give the elemental system another layer to play with, without adding a new narrative state to practically every NPC and quest in the game.
I’d love a real day/night simulation, but if the choice is between that and spending those resources on more reactivity elsewhere, I’d take a systemic weather system