I think we need to remember to avoid the pitfalls other similar mechanics have had, though.
Punishing some realms will not necessarily make them got to war.
I do have some growing concern for realms going "well, we've got our regions, why bother invading the neighbor?". And, well, everyone doing that, because given how many nobles all realms have, in most cases, realms would surround themselves with rogue regions if they aimed for a density target.