Insignia for your men as they level up, according to nation.
For example, for russia first rank would be: Красноармеец; red-army man.
For germany it would be Schutze, or Soldat
and for USA it would be Private.
As your men get better levels the rank goes up, and the uniforms would change. This is not entirely necessary but it is a good detail.
Another thing would be, an officer class unlockable with each campaign which would provide buffs to your allies within a certain radius, (15m, 20m). These buffs could be health boost, stamina boost, aiming accuracy boost, etc.
Thank you for reading and I hope you add this into the game when the time comes !