Indeed! Moar Black Death naow!
As others mentioned: I wouldn't mind a Late Middle Ages DLC. It's way more needed than early game ones (Charlemagne...). A a late game DLC should contain the Riders of the Apocalypse (Late Medieval crisis: famine, disease and well... war, but I guess war is already in the game) and the gradual transformation from feudal to early modern states. Kings get more power by f.e. allowing a larger demesne and allowing to have more than two duchy titles while being a king. That way he gets more direct control over his kingdom in a way that's pretty close to how it was hstorically. Though, there should be some variation, seeing that the HRE lost power in the same period whereas the Imperial vassals gained power.
Also, if realms would tend to become more centralized in the late game, they should be less so in the early stages of the game. I still think kings are too powerful at game start. They shouldn't be able to raise levies from their vassals, let alone tax them. What happened to "Le roi doit vivre du sien"? (English: "The king has to live of his own [possessions]") In other words, the monarch must live of his demesne, not take anything from his subjects apart from occasional 'bede' (Dutch term, don't know the English variant. If anyone could translate, please do so. I'll edit this post then), which, on the otehr hand, only started from 1200 onwards.