I used to play Supreme Commander and there are some feature in that game making base building and unit management much more convenient. I think AOE4 could benefit a lot from implementing some of these features:
Building templates: allow the player to specify a group of building in a certain layout as a template, then the whole group of building can be placed with one click. Late game economic management would be so much more convenient if we can place a mill with 8 farms around it with a single click.
Ferry: assign a ferry route with two points in a map with transport ships and units sent to either point will be automatically picked up by the transport ships and drop off at the other point. This could also apply to rams and siege towers.
Auto control grouping: units produced from a production building are automatically added to a assigned control group when produced.
Auto-queue: production buildings will keep producing the specified unit when there’s resources available. In Supreme Commander, the player can even specify multiple different units in the queue (ex. 2 knights and 1 horsemen) and the building will keep production the specified composition of units.
These features are mandatory in Supreme Commander since the player could be controlling 500 or even thousands of units in that game, which is not the case of AOE4. However, I think these features could help the players focus more on the macro and strategy and spend less APM on repetitive management tasks if that’s the design goal of this game.