Sure, but why bring that to BG3 when you don’t even do day night cycle?
A conversation system is already required for the main game. Talking to the dead and animals is merely a conditional way to access that system. That is a far, far simpler thing to do than to create a day/night system which the world reacts to, and developing that system takes a lot more resources and time than the conversation system (which already exists and is a refinement of what Larian has done for their previous two games).
The amount of content needed for speak with dead and speak with animals will be tremendous, but that's the content. The actual system is simple and already exists. Not so much with a day/night system. Even if nothing else reacts, the stealth system would need to work with day/night.
If a day/night system makes it into the game, it'll likely be later into development, and they would not want to announce it unless they're sure they can get it working with a reasonable devotion of time and resources.
