I'd imagine it would be fairly difficult to actually balance Atilla in the game. I haven't looked at the period for awhile, but the only reasons I can remember as to why Atilla was thwarted from actually conquering the Western Roman Empire was the fact that they were much more valuable as an intact golden goose (at first), a combined Goth/Vandal/Roman alliance which beat them a grand total of once, and by the end of it, simple logistical limitations (they were nomads, and as such did not have any real supply lines to keep their armies fed, instead choosing to forage off of the land, which eventually grew unsustainable), disease, and essentially being bribed by the Roman Christian Church to just go away.
Guess it could work if you implement all of this into the gameplay: make food gathering a much more limited and difficult-to-maintain tech tree than the other factions, maybe do what Alexander did and have Atilla being routed/killed an automatic game over, maybe tie army morale with just how much plundering and looting they're doing, so if they spend X amount of turns not killing shit they'll start growing restless and either rebel or desert, etc.
. It's kinda like a proto lets play of a M&B Khergit vs Nord battle.
I can give you a list but just google "Turkish Star Wars" its the best of best.
