I really don't understand why those nations are not available starting with Industrial age at least. Those nations shouldn't be missed out, especially with regards to World war 1 and 2 when they were among those with the most powerful armies.
I agree with adding Russia/Rus, where it's nation power can be solely about more men and unique unit be calvary, but I always feel that US is more like two nations, Natives before and English colonists after. I won't mind if it is added somehow though.
I think we don't need additional nations anymore.. the most important is Nexon BHG focus to expand and add more features of the existing nations such as 2nd unique troops of each nations.. if Nexon BHG add new nations, players especially advanced players will confuse to choose what nations suitable and best for them..
I am much more inclined to balancing existing nations than giving them additional unique unit. It is, in fact, bringing up to the table of having more difficulties in balancing nations in which the British(a nerf, +1 range but giving them bonus damage is absurd), and the Greeks(a rework, more players rather go French because of the stats being shared) unique units is in need of along with weaker Nations needing reworks