Hmm, this is certainly an interesting concept. Right now, as the game stands (and in most realms I suspect) the nobles put way too much value by the realm. This sort of thing would very much encourage people to look out for themselves, as well as encourage more wheeling and dealing. The regions would be loosely aligned by agreements no doubt, but not part of the same realm, so the (players) would not feel so obligated to follow realm loyalty.
However, the message system would also need to be reworked a bit I guess. A "realm-wide" message would certainly not have the same value...
