I'll just throw in a random suggestion here.
I've been thinking along similar ideas but was leaning more to an app (Website fit for mobile use in this case)... Everyone loves a good app, don't they?
The idea is as follows:
You have been attacked and want revenge but you only fly freight? Not a problem - Use the app to report the player whom you want to place a bounty on and the amount you are willing to pay and how you were killed - Reason for revenge.
Budding bounty hunters can then see who is wanted and by whom plus the price they are willing to pay in commodities (Gold for example).
The bounty hunter is required to provide proof in the form of a screen shot or video clearly showing the destruction of the wanted commander which he can then send a link to via the app so the original bounty poster knows he now has to pay and can arrange when and where this is to take place.
How will you know if the player will actually pay you? A system of reputation can be built in so all users that do not pay will get a black mark against them to warn others they may not give you the readies and of course the bounty hunter can also place a bounty on their heads for not paying.
This would allow for not only groups but also lone wolfs to take part and help those looking for retribution!
Still fleshing things out and who knows, I may even get time to write it one day...