It'd be interesting to see if you could add some sort of AoE check which checks for player deaths. That way, the chest could be configured so that it can only be opened if there has been some bloodshed nearby. It helps encourage player versus player and helps prevent randoms opening said chest.
I imagine it'd be easily to implement another line of code alongside the distribution of PKP which assigns a variable to the player for a thirty-second period or so which then grants the ability to open the chest. I.e. you must kill a player within the last thirty seconds before the chest can be opened.