This is just some stuff I think would be cool to see in a dedicated bubonic plague DLC but I don't know a whole lot about the bubonic plague so if any nifty history knowledgable people want to chime in with some plague related facts and ideas that would be super cool
So plague should effect cities that don't have very high technology stats the worst, things like city walls or military stuff
There should be different severity of plague the higher the severity the smaller levy you can raise and full blown plague will cause no levy to be raised.
More heresy's pop up as people panic
Events involving Flagellants
duchey's that don't have the plague will declare independance from larger kingdoms that do have the plauge to stop it transferring.
Trading will stop. bringing in less money.
Peasants revolts happen more often.
Mercanaries cannot be recruited in high plague areas.
Armies that fight in plague territory can bring it back to their home country upon return
characters that gain the "ill" trait have an increased chance of dying.
Characters have increased chance of getting the ill trait.
Hunts, feasts and wars increase revolt chance significantly
New position opens up for characters who have high learning for plague doctor to steam the tide
Terrible idea for DLC.
Mainly for the fact that its not modular. This isn't something you could exactly limit to those who have bought the DLC, like Mongol faces or extra songs. It would be silly if player 1, the King of France, is being wracked by the Bubonic plague, but Player 2, the Holy Roman Emperor, is completely fine because he didn't buy the DLC
Harrowing of the North... so basically you want a scorched earth ability? I don't know if I would call it increase to support limits. It should depopulate the province and give it a bonus to culture shift. Possibly it should also remove the lord to be replaced with one of your own upon the peace deal and it should destroy one of the small holdings.
It would also allow you to cripple an enemy for a while and leave them with the ashes to rule over at the cost of tyranny in a non-conquest war. I think it should also give a "Furious" relation modifier. Possibly upset the Pope if they are Catholic people you use it on without a Papal Sponsored invasion? If used during a Papal Sponsored invasion it should blemish the Papal Authority.