Yeah I like this feature list, I agree those are cool things to work towards and will be new for those stages.
I think there’s interesting stuff we can do with them using microbes. For example with armies we could have each army be a cpa patch which is connected to the province it is stationed in. This means the “people” in the army are modeled and so are their “horses” or pack animals and “cats” and “dogs” following the army and the microbes that are with the army too. I think that could be super interesting as the army would interact on a biological level with the area it’s in, getting diseases, eating different local food, hunting animals, which is very realistic.
Same with managing cities, managing the life in them could be really interesting, like how sanitation might debuff microbes or using too much wood decreases habitats for local creatures and stuff.
Also if provinces are a cpa patch then trade routes can connect them which means creatures and microbes can spread between them. As technology develops your wold gets smaller and that spreads different species around as is realistic. Like new crops from other continents can be grown in old areas and that growth can be modeled with cpa, also there can be invasive species etc. Like you introduce “potatoes” and they grow great giving you lots of food until the local microbes adapt to attack them and then you have to deal with crop blights etc.
So yeah I agree with you, I definitely wouldn’t want to detract from any of the features you mentioned and yeah making a solid strategy game is important. I also think we could make some really unique and awesome management gameplay if you’re trying to actively manage cpa patches as part of the game.
I’m just spitballing here, so this may not be a great direction to go in though.