My one complaint with the new system is that adding new Duchies requires some acrobatics with a Duke who has got nothing to do with the new Duchy - only the game doesn't know that.
When I conquer a new stronghold/townsland/city, it gets added to an existing Duchy. That means that the only way to make a new Duke is to get the Duke I want appointed to the new region by the Duke of the existing Duchy, promote them (so they are now Duke + Margrave) and then ask them to shuffle over to some other region if I want a Margrave different from them. Unless I'm missing a piece here. So you end up in a weird situation where the Duke of New Jersey gets to decide (practically, if not legally) who the Duke of New York is going to be.
It should be possible to create new Duchies even if there is not a lord in the "home" region.
