Having fooled around with the mod a little I have a wish for a feature to be implemented; a game rule that disables advanced succession laws until the required tech is researched for them, currently the Visigoths start the game with High Partition and the Roman Empires, all of India and probably also the Erenshar with Primogeniture. I understand why they have this from a historical perspective, but it completely breaks the game.
CK3s balance is not designed for anyone to ever have primogeniture and without the player interfering realms who have it will almost never collapse, instead they will slowly gobble up each other through intermarriage until you end up with a handful of giant empires splitting the world between each other due to certain faiths being incompatible, without the dynamic tension created by realms rising and falling the game becomes rather stale and an AI with primogeniture won't experience realms falling.
While it may be historically accurate for certain realms to have primogeniture, the results of this coupled with the CK3 AI produces wildly ahistorical results.