I've made a mod for faction exclusive unit upkeep rebalance but I think unit upkeep rebalance could be settled across the board.
Elite cavalry is far too expensive which means you might as well just settle with mounted lancer militia for the entire campaign. This is something which I think could do with serious adjustments - potentially cutting from 400 to around 300 for example.
I also think that elite infantry is largely pointless because heroes are far more powerful than them. So I think they could be rebalanced so spear guards aren't the only most viable unit in the game.
Do you have any ideas on what units should be rebalanced?