I'd like to see the PK system set up like Meridian 59.
All players had a white name, meaning they were innocents. If an innocent attacked another innocent without killing them, their name turned to orange, and they were labelled an outlaw. The consequence was simple, one you died one time as an outlaw, you were returned to innocent status.
However, if you ever outright killed an innocent player, you were considered a murderer, and your name turned to red. A murder could be killed on site with no consequence to the attacker, and the murder would not return to innocent status, unless a Justicar pardonned him/her.
I left a lot up to the community, while being a PKer was still entertaining, it was dangerous and carried heavier consquences than just flat out griefing.