Here's some small suggestions:
1. Make theocracy characters (priors, priests) spawn with the priest specialization (lvl 1-3) and allow them to upgrade the specialization passively through their job events (charity, proselytise)
2. Allow good enough mages (lvl 2-4) to practice certain specializations on their own (much slower than in a guild, would even require money for research material)
2.b Could probably expand this to all areas and their specializations in some form or way.
3. Combat traits (inspiring leader...) should be limited to max 3 per type or else the UI needs a rework to accompany more of them.
3.b (Fix) to the combat trait upgrading. Right now you get a bunch of lvl 1 combat traits and you cant upgrade them.
4. An event to make sure that the Arch-Mage of the mages guild would always gain the mages guild duchy to keep it from falling to random courtiers with martial focus.
4.b Maybe even an event where the council votes a new arch-mage.
5. Make AI much more likely to join same culture/religion rulers vs invading foreigners in defensive wars. This would make invading other provinces much harder until you unite the province you're already in.
Seeing Skingrad expanding to Elsweyr or Anvil expanding to Hammerfell before they have even united their own kingdom seems immersion killing.