Hm... I'm in favor of a war-system, but Ed, I think your approach would be too complicated and complex - practically adding a new section to the server, or replacing it entirely...
As for a system, I think it should at least have the ability to assign a battle-zone (say center, north, north-weat, west etc of each kingdom island), prevent respawns there while the battle is lasting, allow for the use of magic and prayers, maybe in some way restrict enchantments on armour, and add a kind of uniform look to the kingdom members for easier fighting - say a special helmet or something. That certainly leaves a lot of space for additions... and I think forts should have some kind of heavier weapons to fend off attackers - I'd love to see a catapult in action, raining tree seeds on any foe
