Sounds like a good way for rulers to get candid anonymous feedback, assuming it would be anonymous. But make it a fluid ranking system, like a 5-star boredom index and allow players to change their rating whenever they choose. I'd also be in favour of making the scores public, for the benefit of players looking to join or leave a realm. Instead of requiring a declaration of war, I suggest allowing the players to decide when to rescind or change their rating. War is good, but not meaningless hasty wars without any context. There doesn't need to be an IG mechanism to punish boring rulers, because the boredom index will either nudge them to make things more interesting, or bored nobles will migrate to more interesting realms.
