Indeed Seirun. Actually, the only faction I am planning to add, right now, would be some kind of Cavemen. All complete with their own language the player would have to learn in order to interact with it, and bringing various interaction improvements: access to rare ressources, some very special troops to recruit, and some kind of quest/storyline, maybe trading some faction unique objects, unlocking some long forgotten secrets if you become friendly enough, and so on...
Keep in mind that rigale is really not about adding more stuff, but adding more NEW possibilities and interactions to the game...