How about a mod set in Asia Minor during the time of the Galatian settlement? The invasion was as thunderous as the Cimbri and Teutones' movement. This could include all the incursions that were made by them in the region, and the major conflict with Pergamum. The Galatians could be represented with a unique hellenised culture, with more greek type armour than traditional Gallic, like the Gauls of Masillia.
The three Galatian Tribes, the Tolistobogii, Trocmii and Tectosages would all be separate allied factions, or there could be regional variant units that could define the tribes instead. I think this could be one of the last mods in the 'traditional' rtw map that hasn't been done.
A few pics of Galatians