So far we cannot add new factions. Nobody knows how to. For now we are focusing on the things we can improve like stats, units, campaign map, buildings, resources, cultures, etc...

In the future we were hoping to add as many factions as it would be historically correct to have depicted in the 270BC time period. All this according to their importance and influence in History. Of course that a great deal of this will depend on CA's patch and expansion release and not on us. Only the future can tell...