Well you're the one who came up with the Shi'ite heretic idea.
So it's more a combination of all three!
I'm curious if there's any way to spice up the rebel shi'ite presence. I'm kind of inclined to suggest we feature two/three rebel factions. One for the Christians, one for the Muslims, one for the Mongols/Timurids. For Christians it could represent simply ambitious lords who try and establish their own outremer kingdom (Or lords who interfere in Georgian or Armenian politics. I believe one of the crusaders 'became' king of a eastern Christian city), for the Muslims it would be Shi'ites, and for the Mongols/Timurids it would be..well, generic rebels.
Idealy it'd be nice to have two sets of muslim rebels, one for far eastern (Transoxanians/Ghaznavids/Delhi/Abbasids) and one for near eastern (seljuks, Rum Turks, Ayyubids, maybe the Abbasids). But that'd require adding in additional code for each unit we want them to have in the battle.model. It'd really be a question of what can be gained by having two sets of Muslim rebels and whether or not we think in the future we might have use for those two faction slots (I doubt it, we have 30 faction slots and we've used up only 16)