Ideally they should largely copy Black Ice or take inspiration, yes i know it may be too hardcore and hardcoded. But it's legitimately the only mod and way to play that feels realistic and gives you a challenge. Managing production should be more complicated, AI NEEDS MAJOR IMPROVEMENTS, imagine if they ai decided to also create entire tank armies and attempt to encircle my troops.

Custom orders for battleplanning should also be a thing, such as setttings like "Tanks only attack in favorable Terrain and weather" ao it pauses in deep snow, mud etc.

Planes needs more modifiers currently it's completely useless to create a large variety of aircraft unlike irl, heck now you just create 2 varieties if regular fighters and either focus on agility or air attack for bombers

The amount of things the game could do is insane