I just got done reading some posted suggestions and find them nice. I am indeed all for the whole remove tribal invasion for people with four or more counties. Once you get that big, you're kind of already unstoppable. Maybe two duchies is a better example. Maybe. And the barbarian culture thing, I may implement, all characters and provinces will change to the culture named after the Kingdom (sort of works like Mongol conversion). For Empires... still not sure how to go on about this. Instead of how many Kingdom titles you hold, I think I may make it an event that fires if your realm size is a certain number. Vassals not being able to declare Holy Wars or Invasions is something that needs to be done,
However, I want to post some suggestions as well as you THE PLAYERS will get to experience. For religion spread, it may work like Mongols. The religion will randomly emerge at its "capital". Neighboring provinces that are pagan will have a high chance of becoming that religion, and lords can decide to convert (AI will probably always do this unless has zealous trait.) I don't know if I want to do this like Mongol Conversion in which every vassal and province under that character will also convert to that religion, or just have that as a different event where the character can decide to do force conversion. As for the religion capital... There's two ways to approach this. One is the historical way where I just have the religions begin where it did historically. The problems of this could be uneven spread. Ideally, Christianity would eventually split, as does Islam (this might be very hard to do.) The second approach is to just place them in the four corners of the map (not literally) and have them emerge at the same time. This is probably the easier way to do it. I also want to change invasion CB so it doesn't necessarily work like the invasion CB. Instead, it will work like Muslims Conquest (but will be called Tribal Invasion because it just sounds cooler than Tribal Conquest. Tribes don't conquer places. They invade the hell out of you.)