In alphabetical order:
Alans: They’d represent both the Western and Eastern Alans, as well as the Sarmatians, but their Wonder and architecture would be firmly Caucasian, representing the Kingdom of Alania in that way. Their campaign would be Goar, the Alan general who helped some Roman usurpers in the last days of the empire.
Azeris: They’d represent the people of Azerbaijan, but this one is more of a stretch, since they were mainly subjugated and neither resisted nor conquered anyone to my knowledge. Their architecture would be Central Asian.
Circassians: They’d represent the people of Circassia both before and after their unification. Their campaign would be Inal the Great, the ruler who unified all the Circassian tribes. This one might be challenging in terms of AI player names, though.
Durdzuks: They’d represent the Vainakh people in the parts of the North Caucasus that weren’t occupied by the Alans, like the kingdom of Simsir and the regions of Chechnya and Ingushetia. Their campaign would be Khour II, or Gayur-Khan, a commander who opposed Timur during the invasion of the Caucasus.
Khazars: These guys need no introduction. They’re the most natural fit for the game out of any of the ones I mentioned, as they had an actual empire with actual power. They, like the Azeris, would have the Central Asian architecture. Their campaign would be Tong Yaghu Khagan, a Gokturk general who worked with the Khazars to beat the Persians during the Third Perso-Turkic War.
Well, what do you think? Are these good choices? Do you have any more? Let me know!