The bounty system is great, period.
Furthermore, having npc's hound the gank-er makes his life all the more rogue like, making the game itself interactive with his persona.
It would create- a piracy/bandit/criminal style of gameplay.

Then you can create dangerous area's designed only to accept criminals with bounties* and criminal backgrounds, like basically, creating a faction you slowly get accepted to over time.

Perhaps even, a faction who has benefiting quests/player interaction along the lines of the ganker's interests.

Imagine a daily quest enabling the player to gain things from eliminating players within limits of the faction areas, or assaulting a normal city. Accruing faction from killing city guards/police.

So on and so fourth, be the bad guy!