PVP in DW?!

At first I thought "Rocks Fall, Everyone Dies" or something similar, because on the one hand, no one likes having their campaign spoiled by petty squabbles. I find that PVP often has a one sided instigation. That being said I can see merit in rewarding the level headed player. Instead of outright banning PVP, I offer the following:

• If one player rolls Hack and Slash, getting a 7-9, and the other player chooses not to act on the opening granted, the passive player marks XP.
• If a player chooses not to retaliate when another player's Volley puts them in danger, the passive player marks XP
• If one player chooses to roll +Bond they mark XP.
• If both players choose to Roll +Bond at any point, the fight is over, their bonds are resolved if the actual RP permits it, and they get to make new ones, and mark XP.
• Players may only ever mark XP from one PVP. If they engage in another, with any player, they can't mark XP. 

It's up to the GM whether future PVPs require the instigator to sacrifice the character or not, or whether they'd use this rule in the first place, but I wrote it, so it should be taken as a given that I would.