Just a few more thoughts...
I'd like the ME to actually portray what I find to be very determining for the region: BOTH homogeneity and heterogeneity.
There is a certain aspect of religion and ruler class similarities, most notably in the form of (sunni) islam which is very much determined by the society it had been "created" in: it's not for nothing we have terms like "the arab world".
But even though this IS the case, having only this perspective does little justice to what is also very prevalent in the region: a rather extreme heterogeneity in the form of different peoples, tribes, religious interpretations; history and tradition. Some are influenced by the mongolian steppes, some are remnants of the old Assyrian empires, while others are Christians or pre-Islamic religions mixed with obscure islamic schools.
To adress this duality I think we need two things.
Firstly:
- (new) Diplomatic mechanics representing the vying for hegemony and homogeneity. Basically claiming the title of caliph - and the legitimacy and political agency (or lack of) in doing so.
I think this can be done by "mixing" existing mechanics into region (or religion) specific mechanics. I'm imagining expanding upon the scholars while drawing on the hegemonies but with weaker bonuses - especially military boni. Rather than boni, let's have some diplomatic interactions reminiscant of the HRE-interactions, extra dip slots, and some mechanic that DIPLOMATICALLY allows the hegemon(s) to influence surrounding nations or followers of Islam.
Ideas for hegemon "influence" over the ME/islamic world (some should probably be mutually exclusive):
- Negative (or positive) modifiers for heretics/heathens
- Skewing Dhimmi (heathens) modifiers either negatively or positively
- Send 10% yearly manpower to brothers in faith warring with either heathens or heretics
- Strengthening propagate religion impact (could also be tied with some trade range/trade steering)
And perhaps if the devs have allocated enough time to this expansion: a new form of vassal that are a non-integrateable mix between vassal and tributary. Would be great for Ottoman relation with europeans, but likely also in other cases.
And secondly:
- More cultural diversity representing... Cultural diversity.
Whether we like it or not, it is probably too late to introduce dynamic culture, pops or the like to EU4. But this can be done rather easily with existing mechanics: basically split up more culture groups, particularly the Levantine group into two or (preferably from an ethnological perspective) more groups. The easy fix without adding cultures is splitting it into two: arabian peninsula+egyptian+syrian for one "pan arabian" group and a turko-mesopotamic group with the rest. Ideally add several one or two province cultures tied to both religion and language: "nestorians", assyrians, yazidis and the list goes on.
This will obviously result in more unrest in the tags occupying the region - especially the Ottomans. Which seems historical: in the current shape I think it would be perfect, since they'd likely not have much troubles dealing with it, but it would still undo the ridiculous lack of uprising in the Ottomans. Occupy them for 20 years and give them 20 WE and they still just get particularists and peasants...
We could also strengthen the Dhimmi estate, and make them more relevant if they're also a part of the diplomatic hegemonic mechanics I suggested above, while compensation for the split of culture groups: "happy" Dhimmi could give +0.5 tolerance heathens/heretics and alternatively (or additively) -10% unrest from unaccepted cultures. Ideally it should not make up for the split, but give the player or the randomly competent AI a chance to mitigate the negative effects from smaller culture groups.