game mode like ww1 / ww2, two trenches, the aim being to take over the other teams trench / kill all their players.
would have to implement being prone, or utilise their full body tracking to lie down to crawl through no mans land, through hellfire and machine gun bullets raining down on you, and small tunnels leading to the other teams trench (or instead of small tunnels prebuilt, a mechanic of shovelling dirt from the trenches to the other teams trench.)
could be very fun gameplay, limited ammunition, squads of 10-20 each, nothing de-spawns, and limited lives. Injuries require the appropriate medicine/treatment, realistic gunfire and atmosphere. Not capture the flag, ACTUAL trench warfare.
two machine guns per side, bolt action rifles, mp18s, 1911s, webley revolvers, ect.
Damp, foggy, low visibility, can only see name tags of friendly players, dark, night time mode could introduce lanterns or matches to see, think all quiet on the western front, but with more variety of weapons and time of day can vary.
Could also be a future mod, but I think would be a very fun in-game gamemode.