Unfortunately, terrain shadows are still hardcoded, and it's hard to change terrain illumination through textures, because smooth transitions would require an enormous amount of textures. So there needs to be a better mechanism for terrain lighting before we have a full-featured day-night cycle.
That's a cool concept, simulate time passing in game (reminds me of that person simulation game by EA Maxis). I guess this would be some future enhancement to change to make it happen. Other older games had different appearances of time i.e. Tiberian Sun with: Dusk, Dawn, & midnight I think? However it was static during the match. Maybe that could be the first step before making it dynamic?