Working off of another idea I think from the new combat package (I skimmed it, so it's probably just a couple random words I remember), what about making each region type have some sort of specialty, unlocking more as more knights take residence? It should be something necessary for typical well-functioning realms, but not something that cripples realms without it. The benefits will accumulate rather than being exclusive per level.
Something similar to this was planned as the heart of the old estate system, and still something that could be done with the new estate system. Knights could build buildings on their estate, each one having a certain effect. The buildings would only function if the estate was occupied. Larger estates could have more buildings. Buildings would be provided that benefited the region, or benefited the knight. (IOW - One building could gain the knight +2 prestige, another could increase morale in the region by 2%. No building could do more than one thing.) Unfortunately we never really nailed down exactly how it would work, let alone iron out all the details. Feel free to flesh out the details. They could be transferred over to the dev wiki, and archived for future use if it ever gets worked on.
