Now this would add a lot to the game and has been asked for a long time now.
Raids would be more scary because you don't know when or where there coming
You would need to scout out the land and/or make and detachment from the main base
At night you would need flood light or flash light to see anything
Maybe patrols to see stuff
You will be able to see all of your home zone
You can only make home zones if you built something close to it or just have separate zones
Maybe add something hidden like tech or buildings that
Night raids would mean something other then just it being more blue
This would give new life to the combat system and the game as a hole
I'm not really feeling it myself. It would be super annoying to have hidden snipers or besiegers you can't locate.
Im not to sure how all that would work i could find a way to fix all problems but naa. and if this idea were to be added to the game/mod you would need to be able to turn it off if you didn't want it in your game.
Tynan has said it's already programmed into the game, or was. I think it's inactive and incomplete.
Right now he's working on more manageable things instead of spending a month getting it to work.
But we can hope for it as an option or as a mod someday! Keep pushing for it :P I think it sounds fun.
Fog of war would be interesting, but there are a few key points you've left out.
This one's a pretty standard RTS mechanic - if something that isn't specially hidden shoots at you out of the fog, it gets revealed temporarily (long enough to stay revealed between shots, but short enough to fade away so as to circle back around and strike at you from another direction). Once a mortar fires, it would have to be permanently shown.
If a raid appears, you need some way of know where the main force is, without sending people out in the open where a single m24 round can end them instantly. This would allow you to prepare for an assault, but still allows raiders to send out small groups to flank you, harry your defenses, or even sabotage parts of the base away from where the main force is attacking so as to distract you, without letting the player know exactly where their away parties are.
I would have to question tying vision to the home zone, that would probably be too easily exploitable. Even if you were limited to building within range of your own structures, there's nothing to stop me from covering the map with stone pillar "sentries". And an arbitrary limit on building within range of other buildings would only serve to annoy people.
I also definitely that it should be optional, as it would create a pretty big difference in difficulty, especially for newer players.