Civilians
1. Instead of farming just for resources there could be the option of farming for civilians.
2. You could transfer civilians between cities just like resources.
3. There could be an option to use coins to regenerate civilians.
Also a few other ideas I have had
1. There could be new tech skills for indivual army types, eg: one for inf, one for cav, one for arch, one for cat.
2. Maybe an enhancement tech skill, the higher the skill the better chance you will have of successfully enhancing your equiptment.
3. Also a hunting tech skill to improve hunts, same as enhancement, the higher the hunting tech is the more successful the hunt will be.