In my opinion AoE4 will be the best game to showcase this AI. Specially because on how many different strategies it is possible in a RTS, where units have strengths and weakness.
I think will be a kind of AI based on machine learning, where during alpha and beta tests will play against players in order to learn how to win. In the beginning will be boring and not challenging at all. But with the time the AI will evolve becoming harder and harder.
But the AI cant evolve itself, will need good players playing the alpha and beta in order to improve it.
The diffucults of AI will be based on whatever metric they used to evaluate the AI evolution.
When AOE4 be released probably will have a difficult called insane where the perfect micromanegment will be unstopable where you will need at least 2 players to take down the AI.
Balance patches will probably make the AI test new things like it does with players.
Lets see what the future will bring