Are there any features from outside the Age of Empires franchise that you would want to see incorporated, or feel like didn’t work well?
For instance, in Empire Earth 2, it was possible to use a picture-in-picture window to see two screens at once, which could let players quickly respond to alerts or monitor their base while controlling units elsewhere. Although I felt like this was great to have as a lower level player that can’t respond as quickly to alerts, I don’t think it would work as well from an esports perspective (it might be too busy for viewers).
I did like EE2’s citizen management system, which allowed you to assign villagers to a resource and let the AI handle the rest. You could right click a resource on the UI to untask a villager, and left click to drop them to another resource. They would move to the nearest of that resource available and start collecting it. You still needed to micro to place collection buildings, but it made quickly correcting economy issues while in a fight much easier.
It was also possible to create custom civilizations in that series, which is something I don’t want to see return in the same way. I like the idea of some civ bonuses being selectable (like in Age of Empires Online), but choosing all of them created a cookie-cutter meta of the best build possible selection that actually lowered variation. I would prefer a smaller civ list with different feeling civs.