Honestly I think what would be the most important is new battlezones. It gets tiresome after day 1000 you’ll still be fighting on bare grass hills. When I attack a castle of bandits, they should start in a castle, perhaps even with archers placed in towers. This could require even new skills in order for siege battles.
Battles on ships should also be a thing, you could force the men to make casual initiative rolls during battle, or they’d fall which would make them unconscious for a round. That way people would also be more tempted to use light armor on ships.