People can still damage the regions production, make morale go way down, damage recruitment centers etc. But it should in my opinion have a lowered effect on realm control. Looking at a map and seeing huge boarder [sic] regions that are just rogue rubs me the wrong way.
So if, under your proposed change, you can still heavily damage a region to the point that it's a burden on your enemy (low production and therefore small harvests, but still a relatively large population), how will this encourage people to do takeovers rather than looting?