Could build it off of the Hunt Board as this is what it sounds like to me, just with additional steps and difficulty. Would whole heartedly disagree on the instanced portion though. It's already getting a little dicey with instances and the current population, throw a new expansion on top of that and you windup with Rhaubahn extreme all over again.

Could make it so that other people simply can't attack your target, but then it opens the door to it being cheesed through people buffing/healing you.