The general idea is kind of neat. As another requirement, I'd suggest having a minimum in game time, as well. Nothing astronomical, just enough to ensure existing characters are the ones to do this.
Also, perhaps have it restricted to Guard IDs by default? Then also have it check names (and have a system to authorize groups of varying sorts); If they have the necessary portion in their name, it would allow them to also do so? This would kind be a negative for the various independent IDs, but then if they're not part of a larger group, who are they asking to kill said target?
Combined with a bounty system, though, I think things would work out nicely.
![[Image: 4986_s.gif]](http://signavatar.com/4986_s.gif)