I have thought about this for a long time. I think there should be some 1 on 1 PvP system, where if a knight has some rivalry (for instance simply arguing, or wanting to fight just for fun.), then he/she can go to a dueling arena, and send a "challenge" message to the player he/she wishes to fight.
This has been suggested multiple times already, and frankly, I don't like the idea.
Firstly, "defeating" an opponent doesn't mean you're more skilled than him. Gear efficiency has a much bigger importance over who is killed.
Secondly, X1 can be frustrating sometimes, especially for kids, which seems to be SK's main audience.
Finally, the game is based on co-operative and sometimes competitive gameplay, not childish arguements and humiliations.