Okay in my opinion i think their is an easy solution to this a separate server/ channel that has the PvP that you must manually turn on by going to setting and activating PvP. In doing this your risk all money you have and if you dont have any a random item in your inventory. You can only force fights with other people that have red names ( the red name would indicate their pvp is on). Now to avoid people just starting fights and then leaving to a different channel, once you force a fight you must wait a 12 hour period where u can only be in that channel and must have your pvp activated.This would make it so that if you abused it and killed som1 you would put yourself at risk for a period of time this would separate the random griefer trolls who are to scared to fight people their level from the serious players who wish for a challenge when doing normal tasks.
I think this is the best way to do it without en-raging people maybe my idea is stupid i'd love to hear feedback ^^