I have to agree with Bane here, there should be obviously in game stuff that influences the politics.
I mean otherwise you just form alliances because you like this clan better or rather be on the side of 5vs2 than 3vs4.
Also big yes to raidable caravans, tbh it's the only thing that keeps me interested in strategus.
Some other ideas.
Add some "illegal" trades. Smuggling f.i.
I imagine it like this - landowning factions can't engage in trade on a larger scale. Only merchants who must be factionless can, but factions can tax them. So someone could buy some goods and try to avoid the taxation (simply by menu with a random chance maybe, or factions have border patrols) so he can sell them cheaper in someone elses lands for big profit. This could be a nice way to betray someone you are allied with, working together with smugglers plagueing him. Some goods could bring good revenue but be forbidden or make village output worse (f.e. selling pork in the desert or ale in Nord cities).
Or slave trade, slave traders could abduct people from villages and sell them somewhere else, obviously bad for the owner of those villages.
Add a fedora.
Right to rule stat from singleplayer, maybe with some actions Templars allying with Fallens you loose lots of credibility f.e.