Each culture has 4 faction slots. The only cultures that do not have 4 factions are the brithish,germanic, nomadic and iberian tribes and also the eastern factions. So i believe we will see soon enough new germanic factions (cherusci and chatti propably). Armenia will be an eastern faction, so there will be one empty slot for the eastern factions. I would like to see in the near future an african-arabian pack. Nabteans, numidians, ethiopians and garamantians are good choices.