There I was playing Italy campaign. I've conquered Istria and some other land from Austria and now I'm bordering Ottoman Empire. Suddenly Greece and Wallachia propose alliance though I don't have them in my sphere and hadn't interfered with them.
IRL I'd thought that they obviously think we now have common enemy and it makes sense to gang against it. Or maybe now they fear me and want to secure peace. Then I've remembered recent Crusader Kings where instead of boring diplomacy messages you get pearls like "Hi father, you treacherous pig. I am now declaring war on you." Even better was Galactic Civilizations, where message would be something like "Evil drengins are evil. So if you won't help us in our current fight you'll be next".
So. Wouldn't be good if we get something like that in Paradox games? We'd get more obvious and interesting diplomacy and will see more clearly how smart AI is. If I'd get message like "Ottomans are common threat to us cool christians, so how about an alliance?" I'd have 30% more nerdgasms in V2. Also cheap method cause you don't need to paint additional beautiful pictures to get flavour like those creative assembly guys do.