We need some way for the ruler to be rich. That way he is more like a super-duke. Obviously rulers often had cities of their own in medieval times however I think we need to simulate this sort of power balance without actually forcing the ruler to own a city also (since we don't promote that according to the game mechanics.)
Basically the ruler needs to some way to increase his mojo dramatically, he shouldn't just be symbol for the realm's collective interests. This is more of a modern idea.
The realm has to be able to actually tax cities. That would really be all we need. Yes, Dukes could secede and the like, but most people won't support a Duke who secedes over a reasonable tax rate.
