I wish an Option to attack Factions as a Liege. Maybe make them hidden like plots and that you have to uncover them but every conspiracy with the goal to get independence or lower my authority is right against my throne which I posses in the Name of the greatest Kings of all: God.
Also, for kings sake, implement a second Opinion Modifier called Fear or Authority. This second opinion modifier could be raised by actions that are tyrant or events like winning a succession/independence war. If someone is feared by you he would not consider actions like joining a faction etc. Several Traits like Brave or Coward or whatever could affect this. So a brave Duke is still very likely to join a rebellion even if he as fear or respect for your might though a coward just needs to be feared a bit to stay away from any plot to harm you.
The AI needs some "fear" because as a player you want to hold your land together and so you do not take choices out of fear that you coul fail. The the AI should do the same. It should not calculate "Ah, 50% Levy Size in the Faction... well, lets start!" and then annoy you to death. Also the immersion is broken for no duke seems to think of his own life. He simply do not care if he is seen as a traitor because a frigging tyrant modifier is saving him from the most harm, and sometimes the prison event fires up... just random.
I mean, an absolute crown Law in the 12th/13th Century is absolutely against any history, so why still keep the tyrant modifier?
If you are a traitor, you die! If you plot against the royal family, you die!
Also I would like some "Marshal"-Mechanic. I want to put someone (one of my own vassals) in charge of the military forces of a region to automate several military actions. Its just boring to control a campaign as a player just to bring down some rebel scum, I know that vassals can send their own troops if they are strong enough but sometimes they are not, especially in newly conquered areas. With this action I could make someone marshal of, lets say, southern Iberia. By the kings authority he can raise levies from several counties he has no direct command over (as a duke or else) to face any threat in the area.