From Age of Empires to Age of Empires Online, Ensemble Studios, Robot Entertainment and Gas Powered Games moved the franchise forward. Below are a few of the features I would like to see explored further for Age of Empires IV because they have been implemented in some manner with the previous Age of Empires games.
Customizable civilizations. Age of Empires III had card decks and city levels. Age of Empires Online had city levels, gear and capital cities.
Unique civilizations. Age of Empires had civ bonuses. Age of Empires II had civ bonuses and one unique unit per civilization. Age of Empires III had civ bonuses and several unique units. Age of Empires Online had civ bonuses, several unique units, unique technologies, unique building sets, etc.
Daily, weekly and monthly challenges. Age of Empires III had a web-based leaderboard. Age of Empires Online had Alliance Wars and Sparta PvP leaderboards.
Multiple game modes. Age of Empires through Age of Empires III had skirmish and multiplayer. Age of Empires Online had skirmish, multiplayer, Defense of Crete (tower defense) and Northern Invasion (with MOBA inspired hero unit).
Optional objectives. Age of Empires had relics and ruins. Age of Empires II had relics. Age of Empires III had trading posts and treasures. Age of Mythology had relics which gave special bonuses. Age of Empires Online had treasures.
Do you have any other ideas on how to move the franchise forward while staying true to its roots? Share them below!