Just like ES2 and EL, I wonder if you will have both specific units for each culture like English Longbowman. And the ability to improve units based

on the research and resources you have?  So you have a basic spearman and you have the ability to upgrade weaponry and armour?

Same for a tank unit in the later game. 

Because every culture has unique units, I think it's clear that each unit will have some sort of special ability, and maye the generic era units won't. I think the upgrade system in EL was poor, only because there were too many choices.

I would actually prefer to see a much simpler system with shock, suppression, entrenchment, with these features reducing outright combat deaths and encouraging more retreats, preventing a military steamroll.

EDIT: Here's my proposal:

Each unit gets 3+ slots: Weapon, Movement, and Support.

Weapon is what 90% of the unit carries, and there is usually 1 Weapon invention per era. Spear -> Pike -> Musket -> Rifle -> Carbine

Movement determines speed in the main and battle maps. Cavalry (Horse/Chariot/Elephant) -> Motorized -> Mechanized/Helicopter

Support is usually where cultures get their unique units, or special abilities. This could be a pretty wide category with Swordsmen, Archers, Siege Equipment, Knights, Cannons, etc.