Though CA may make a DLC for this, I do think it would make an interesting campaign to have the era in which the Arabians rose to power. They would start small, but grow in power rapidly. You could play as them and spread your religion across the world, or play as the Sassanids in that you may defeat them before it's too late. The Byzantines and other European factions should also be present. Sorry if this has already been suggested, but I tingle with anticipation!