I like the Hinterlands and the "concentric rings" idea for realm density.
It will I think help to make wars more dynamic as you suggested.
I would suggest that you make such regions "less loyal" and "less hateful" of other realms as well.
The massive peasant rebellions of the East Continent should be far more rare than they are.
Just the word "hitherlands" gives me images of Arthurian Romance style adventuring. There's so much potential for new fun and intrigue.
