I have been thinking about this from two standpoints for a long time. One is the simpler one Im really hoping for firstly, it was an amazing addition in the latest Civilization title and it was great and still is in Three Kingdoms. Im a big fan for small details in games that helps immersion a bit or just looks great if possible. In 4x games the constant day never sat right with me that was common, same with static planets/asteroids and more in space ones. But if we go back to Total Warhammer, I hope we can get to see this happen. I have used mods to darken the Warhammer old and new world as game 1 and 2 released and it looks absolutely amazing when its darker and all the torches and lights pop more. With some work there I think it could be enchanced even more with a steady sunrise, and moon rise maybe some reflektions with a glimpse of the green moon and such. Essentially the lighning change and change of day and night could be a visuall treat. I think while cosmetic it could just add an extra touch to what is one of the most beautifull 4x campaign maps out there both old world and new world look amazing as they are.
Then theres the other perspective and it ties directly into a game mechanic that I have found problematic in the past. Night battles often in the historical titles demanded perks or certain skills to be unlocked and never really truly had its own benefit or impact in my games even if I used them much. I also felt the lightning was a bit flat torches never poped up right and cast light and shadow well and it just been there but not used to its full potentiall. I want a change here for future games aswell. Im thinking night battles for Warhammer could benefit certain factions, undead, skaven and gobblin units and perhaps others like beastmen. In the sence of special buffs, additions to camouflage/hiding and more in battle. Same as day battles would benefit many order factions vs some factions. I wouldnt also mind if the battles had a dynamic clock in the background so a battle map could change to day or night etc and the various buffs and other would change depending on time of day depending on faction. However the problem is of course battle times... how long should it takes when battles arent to long. Is a day 15-20 minutes in game with an ingame option to specify ourselves, sieges could then have a change of light and longer battles to. I do know that rts and many games in other genres have done this for a long time and Total War could aswell. And say a vampire ambush during night time could change if it fails and is prolonged into day with perhaps options to turn the tables around on the enemy if they are a faction that can overcome its weakness with daylight.
I know people want changes to things like siege, I think night time battles and day and nigh cycles is up there aswell and could be a powerful addition not only visually but also mechanically, traits, perks and more and also help add another dimension alongside battle terrain and perhaps if they expand on weather aswell more of that. It could also be a way to bring more grimness into some factions when faced at night say undead and beastmen etc.