I also find the game too symmetrical. What I believe needs to be changed and what I have experimented with changing is the behavior of the bots: small civilizations or vassal states should not act like great powers, and nomadic civilizations should not behave the same way as sedentary ones. The issue, however, is that such changes would make balancing the game difficult, and many players likely wouldn't appreciate it.

What do you mean? This is a mod for modern warfare; the bot will be adjusted accordingly. I’ve included drones in the mod and have already showcased one; there will be many more types, and they will be a key focus of the mod, alongside complex air defense systems. Yeah, I have thought about this.

Building a Market unlocks training Slave class units at the Farmstead and Storehouse. 20 max, but +10 per Market (this is the limit I'd like to make global). The Slaves are capturable and die easily, but are 2x better gatherers than Citizens. Slaves are a gatherer unit only, while Citizens maintain the ability to build. There are 2 technologies specific to Slaves: Slave Trade (-50% train time) and Slave Markets (remove training limit, but Slaves are double cost).   Citizens also have the "Slave Ownership" aura which boosts nearby Slave effectiveness. This basically replaced the old "Allure" aura of the old Female Citizen units.  

"Say hello to my little friend".

What makes a game boring is the lack of variety and the repetition. That it would be more unpredictable, that it would be able to keep you from getting bored and immerse you with its dialogues. A human is capable of using a bunch of camels just because they look cool. Like Hannibal saying satirically: "I use elephants because they are big and look cool in my army, you know there are no elephants in Italy, now they will have them".