These are the nations I know for a fact will appear in AoE4:
Byzantines. (eastern roman empire)
Norse (vikings)
Spanish
Japan
Korea
These are the most requested and popular ones.
Others I might think we may see is:
Turks,
Khmer
Berbers (Spanish Umayyad and Morrocans)
Spanish
Chola (South India)
We may see the Poles/Slavs, but I have my doubts despite their incredible rich history.
I really want to see these as well. but they do pose a very serious balancing question. Especially the native American ones.
How to balance not having cavalry and no gunpowder?
This becomes a rather pressing issue. Wouldn’t have been to much problem in AoE2 as it has more freedom when it comes to realism.
But for AoE4, they wanted History to play a important thematic role to the Civ.
But its also a competitive game that needs some sort of balance.
So finding something that has the key components of: Infantry, Cavalry and Artillery is important. if a Civ lacks either 1 of these, it becomes a major issue of implimentation.
The Seven Fires, the Nahua, and Haida Gwaii.
Native Americans could fit just fine in the game, for the most part. I extended the timeline out for the Seven Fires to the early 1700’s, but the Nahua and Haida Gwaii remain pre-1600’s.