Quick ideas here.
1. The addition of food and water requirements. Some missions can take hours and a soldier would need water and food. This would also have a factor on his fatigue. Maybe some sort of element added so that this would be a factor but not as intrusive as say DayZ. Water can obviously be stored in water bottles, camel packs etc and food in the form of rations.
2. Camouflage netting to be able to put up around buildings and vehicles to keep them concealed from Air & Ground Patrols.
3. Option of setting up concealed OP's if a sniper or artillery observer so soldier can be hidden more and would be more difficult for the enemy to find.
These are just some ideas but I think would give an extra edge to an already outstanding simulation.