What about.. say, a reenstatement of the Yuezhi or a Turko-Protomongoloid race (Forgive me, but I lack the knowledge and resources of the common EB forum goer). Or how about changing the AI Baktrians about the Indo-Greek Kingdoms by giving them Taksashila and making the unit roster more Indian. On that note, we could add the Mauryans, seeing as how they had at least some influence on the Indus valley. But, if we had to choose them, we might as well expand the map to include the rest of Saka territory (Yes, sadly, I went there) and the early Yuezhi, and I bet few people really want that. Well, not in a Roman centric game.

And to those who want city-states and mini-kingdoms in. Look, I know they had unique histories, and had some impact, but if you place an independent kingdom near the heart of the wars between two superpowers, you probably will be beaten quickly into a bloody stain on the landscape. I propose instead to put more signifigant cities and kingdoms (The Numids, the Crimea, Pergamum, you know) into another faction like the eleutheroi, only with the ability to attack cities (Although not as frequently as other powers), raise armies effectively, and build up territory. Who knows, Saba might be replaced with a stronger bandito faction.

Of course there's the problem of hardcoded AI...