I thought of this while on a trip in japan, and I fully fleshed out the entire idea for versions of normal warzone, warzone assault, and even firefight. I sadly don't remember how any of these ideas went. I could probably dig them up with a couple minutes though. I think they went something like this.
Warzone: Same as normal, but two players start as infected with AI flood forms to assist them. Game ends when score limit is reached, or both teams are eradicated.
Warzone Assault: 2 players start infected with AI teammates and must eliminate survivors or capture bases.
Warzone Firefight: Same as normal. Nobody starts infected. Flood themed rounds. If you die, you join the flood and kill the survivors.