I just had another instance in the current version of overthrow liege and independence faction wars resulting in the entire kingdom falling apart after the rebels win. The cause of this is the fact when those types of wars are won by rebels every vassal gets the option of sticking by their liege or going it alone. While this is all fine in good in a situation where say a pagan king loses to an indie faction of catholics that the one or two that stayed neutral would go free on a pagan defeat it makes 0 sense if vassals who dont completely hate their liege or in the case i just saw 2/3rds of pagan jorvik going free just to be eatten right after by mercia no sooner after the war ended.
Can there be somethin added that makes vassals with opinions of just for starters -10 or better of having less of a chance of bailing ( higher the opinion even less) can even add in some traits that add +/- that chance to bail. But more importantly have them stick around if their top liege shares there religion and there completely surrounded by another relgious group ( example assume all of russia is orthodox except for kiev whos ruled by one but all his vassals are slavic. 2 vassals rebel rest stay out of it rebels win the slavs that remained neutral would more than likely stick with their liege since going indie would mean certain death by holy wars).
I think its not such a big problem, this mechanics works well in my opinion, the price of loosing a civil war by decentralised, weak realm should be severe (just like this), vassals dont have to hate their liege to have the desire to "break free" and become independent, and they have the chance to do so the moment the realm and the ruler are in the weakest condition (so during lost civil war). I have only seen one or two really serious destructions of the realms caused by this mechanics, not to mention new / next rulers of weakened realms often reqonquer lost territories. Still, adding a lesser / higher chance of separation based on opinion might be a good improvement.
E: Also, the process of the Christian reconquista in Spain should be much slower...will try to figure out how (I have thought of making limitations who can use the holy war CB and maybe limit them to once per lifetime? Even the conquest of the Taifa of Toledo took decades)
E2: There could be a 'Declare yourself the Caliph of al-Andalus' mechanic allowing you to subjugate the local rulers to represent the Almoravid conquest of Andalusia.
To be honest I dont think E: is a good idea - maybe it could improve thinhs in one way or another according to specific direction (for example who should win and how long should it take him to win), but for me it would make things too "scripted" and arbitrary designed - I mean, I think unlike PB or other mods, CK2+ always avoided giving handicaps or setting special mechanics so that things would surely go acording to specific scenario (for example slow reqonquista of Iberia), It was rather totally random and "alternative", and thanks to that you were always sure that each situation and political balance will be unique and different from another. Giving requirements, special CBs, nerfes or other addons to specific realms would destroy part of CK2+ base advantages, that's just my opinion
As for E2: - which date you have chosen for start? Because, again I don't think there is serious need of special intervention on Iberian Peninsula, Almoravids very often manage to conquer all other smaller emirates (I think they also often have strong claims on some of Andalusia de jure lands) and the balance there between catholics / muslims can really be different each game.