I would suggest some sort of shake up of the relations system that might be able to replace the hostile meter, the cf mechanics and the war stance.

I think it would be possible to do this by allowing kingdoms to declare a number of other kingdoms within a certain range of their own kingdom either ennemies or friends and thus allowing the benifit and drawbacks of hostile/war by declaring them enemies and possible by mutual decleration of enemies unlock a warlike relation for a set period of time with some drawbacks for outside interference, but far less than -75% gains.

In the other end of the scale declaring someone friends would prevent attacks on that kingdom while buffering every defensive stance against that kingdom, while mutual decleration of friendships could allow for some sort of trade and/or regulair aid, perhaps with some drawbacks such as minimum tax of 10-15% on cross kingdom aid and not allowing to aid acres.

Maybe it should even allow for friendly kingdoms to request provinces from their friendly relations to join in on their side in case of mutual ennemities where the kingdoms are below 25 provinces, of course joining in would be optional for the provinces that are part of the other kingdom, and there would have to be restrictions on how powerfull allies you could call uppon.

I'd imagine this could lead to some loose cooporation between kingdoms as well as thougher competition between kingdoms of similair size.

I know this is a bit losely explained and that a lot of factors would have to be ballanced and calculated, but what I want to present here is more the concept than the actual final form of this system.