A thought struck me today while reading an alternate timeline with a surviving crusader kingdom. A way to give Jerusalem some spice would be having a small army with units from a catholic faction spawning in the jerusalem region, with like one feudal/noble unit and one or two faction specific non noble unit. this could happen every 20-30 turns. If you want to make it advanced the factions the units are from might depend on the factions relation to the pope, like it being very high or very low, similarly the army could only spawn if your reputation is high enough.