Theres only three points on which a Bounty system would ever work.

1) There was a proof of kill. That means, like, when I kill MadDog2020, I can take something from his corpse, like his head, or his hands.

2) The game's item trade system was perfect, so that nobody could get screwed out of money or items.

3) The game didn't have any specific or official capacity for Bounties. That is to say, there wasn't a Bailbondsman's office run by NPCs where you could check in on the latests bounties.

This system encourages two things. Mafia style hits and Bounty style vigalanteism. Both, will be contracted either privately or through the game's web forum.

Thats the only way it'd work. Anything more or less and it'll be a pointless system that won't amount to much.