Sure you can do damage to a KD but there is no way in which you can make a province stop hitting. A war can go on for ever even if you manage to drop a KD to 50% of their NW.
If you want abuse there's no doubt that top KDs would use this system to gather honour quickly early in order to help them grow later on, I don't really see any way around that as long as you keep the "can declare on anyone" system.
I'm wondering how you intend to implement this though, what parts of the current relations system would still be in place?
Edit: and obviously you need to make sure that you can't just declare the same KD over and over again.