Two things that I have been really wishing would be implemented in some way, both having to do with core provinces.
The first would be one that would be easy to implement since it was in Europe Universallis III. What I am talking about specifically is the 'renouncing claims' on a province.
Example. France and Prussia/NGF/Germany. Every 5 years it is war, regardless of anything else. Alsace Loraine, constantly for the entirety of the game, truce up, new war, over and over. Would be nice to beable to beat back the other nation hard enough that you could demand them give up their rights to an area so they do not get that free CB.
The second may be harder. What I think would be cool, since this game is more about alternate history then following it to the letter, would be to randomize core events. What I mean is like... USA for example, Manifest destiny. Maybe you use it one game and its historically accurate, maybe you use it one game and it goes north, giving you cores in British Canada, maybe you use it another and it gives you cores south furthur into mexico and forgoes cores on washington and oregon, maybe it gives you cores on the Caribbean islands as well. Could also be said for Prussia, sort of, there are places like southern denmark, or that bit on the west of Switzerland that are cored, would be nice if it got randomized a bit every game so playthroughs were not so... similar.
Every game I see with the USA is either USA conqueres all of mexico and beats CSA, beats CSA doesnt conquer mexico, conquers mexico looses to csa and has a war every 5 years. I never see any variation beyond those few.
Prussia as well, conquer everything and make NGF, dont conquer everything and fall into obsecurity and revolution, get their butt handed to them by austria