I red many ideas before, sry if I repeat those. I hope have more chance at dev team, if more player want the same. : )
Generals Make the game more replayable.
At the start of the campaign, the player get a general, who gives different bonuses in the whole campaign. The general get experience, can leveling. At 2-3 level can choose a specialization. Some example on german side: Panzer general, Infantry ( or Sturm) general, Engineer (or Mechanic) general, Aux general. Each general add new game mechanic, unique units.
Panzer general: anti tank guns and tankdestroyers give fire support to the friendly tanks. If an enemy tank attack the friendly, the AT gun fire first, after that start the tank vs. tank fight. Historicaly german commander offen use AT-s with tanks. Panzers lure enemy armors to front of AT guns and attack back after the AT-s decimate the enemy.
Infantry (or Sturm) general: Infantry units can merge with another ground unit, creating a Kampfgruppe. Kampfgruppes number are limited. The general can require stronger assault infantry, heavy assault guns, heavy mortar artillery, railway artillery, flamthrower units.
Engineer (or Mechanic) general: Infantry and armored units can capture enemy tanks, guns, trucks. The player can use these as core units, or sell, or build new ones. Example: PzII + 76mm soviet at gun = Marder. The types and number of crafted vechiles are determinate.
Aux general: The general can request italian, hungarian, romanian core units with own prestige and deploy managment, dont taking away the prestige and place from german units, but add an extra and free strenght to main army.