I wish they could make better options for AI behavior when an AI military is stronger than you that weren't so direct (that could also be used by humans). For example, in the real world, America didn't just go and overthrow all of Latin America, but for a long time they wielded enormous influence that benefited America. I wouldn't mind seeing situations where some AI leaders with military strength could give better ultimatums -- use/don't use this social policy, choose/don't choose this tech path, build/don't build this item/unit, etc, or we'll attack you. Even doing something like a naval/land embargo without going to war (ie, you sit on their trade routes and they get only a small amount).
I just wish there were more options between middling friend and war.