In the future, when the DLCs for new civilizations are completely finished, I hope to see civilization/regional skin overhauls, plus a few campaigns. The issue of “unit difficulty in identification” can be entirely resolved by adding a button that allows players to choose whether to display unique skins.
Additionally, each civilization has more than one heroic epic, which could be bundled and sold with the skin DLCs. This way, players wouldn’t have to suffer from poor balance adjustments, yet could still enjoy the game’s content. This is my ultimate dream for Age of Empires II.