Maybe this is already in work, but:
I'd love to see complete distinguishable Nations in this game so that they have different Weaponry, Armor and clothing, looks, customization options (height, skincolour etc.), ships, flags, formations, feudal-systems, different trading-goods (e.g. fur can only be obtained in the harsh northern regions, while incense can only be found in deserts etc.), different religions (and ways to conciliate the god(s)), different money, emotes, heck even some skills that are only availabe for one nation only ...
I could think about:
Vikings
Normans
Saracens / Ottoman
Japanese
Hanseatic league or Venice
Of course balancing could be matter, if you make the nations too different, but ..
Wouldnt you love to have a fortress like this?
Maybe there are more pressing matters - but thats what id love to see someday