I've heard many calls for more playable factions in the East, but Attila's "Horde Mode" is just so well-designed - so here's my idea: why not have more playable factions in the East and Africa, but including a unique Eastern Nomad culture and building set and unit roster?
I have a few ideas that I might try modding in, however I've been rather busy so I'm putting my idea out there in case someone else would like to use it. The 4 Nomad groups I've personally planned out are the North African Nomads (Berbers), East African Nomads (Blemmyes), Arabic Nomads (Bedouins), and Sassanid Vassal Nomads (Dailamites, Gilani, and Kurds).
First off, these Nomads should have a different "outlook" in the hands of the AI. They would start out with smaller armies and less developed buildings, focusing on agriculture and raiding countrysides as opposed to diving headlong into the center of the Roman Empire and migrating across huge distances like the Hordes of the Steppe.
Secondly, some would be under "vassal" status and would assist their overlord (Sassanids) in their wars. Some of these things require manipulation of the AI and I have no idea how to do that, so I'm just kind of assuming there are ways to "corner" the AI into doing things circumstantially.
Thirdly, I've only thought of a single shared trait, and that is the ability to take refuge in mountainous, impassable terrain. The mountain ranges would become like natural forts for these nomads to encamp in, and they would get a defensive terrain advantage if any nation were to try flushing them out.
Fourthly, the nomads in these regions (Africa and the Middle East) tended to tax caravans and catch fish (if there was any water nearby). This could inspire some building chains that they could construct while in Horde mode.
Below you can find a brief historical recollection of these Eastern Nomads during the timeframe of Attila.
North Africans
East Africans
Arabs
Sasanian Nomads
Let me know what you think! If you have any pointers to any good open-source models or any other assistance, it would be greatly appreciated.