It would be great if after a certain karma level (or after bombing newbs in the Hub) is attained, a bounty would be placed on the head of the player by the faction with which it has bad karma. They could meet the player in a force encounter where he would have very few chances to survive. It could also be progressive, the more bad karma the player gets the more chance he has of meeting the bounty hunters in an encounter.
1000 karma = 10% chance
1500 karma = 20% chance
2000 karma = 30% chance
After each kill of the bounty hunters, the karma would go down 200-300 (or back to 0?) making it something to think about when doing something wrong or killing regular factions army.
Also, I thought maybe we could have a new "faction" called the 5 suns that are like the judges of the wasteland, meaning that if you have bad karma with towns or other players, they would send the bounty hunters after you. The map is almost ready but it's a WIP and only an Idea. There could be quests related to that and even a new possible profession (bounty hunter).