Just guarantee that high level idiots will not be able to kill low level players, that's all.If max level is 50, so 10 levels difference between players which can attack each other is toooooooo muuuuuuuch.That must be maximum 3-5 levels difference.If mob 5 levels lower that you didn't give you experience, so 5 levels lower player than you will not give you honor too.It's very simple :)
I like the idea of a bounty system or a karma system that punishes players who kill too many low-level players. I think that these systems would create more balance and fairness in the open world PvP. I also think that players should have the option to turn on or off their PvP flag, but they should get some rewards or incentives for having it on. I think that these suggestions would make the world PvP more enjoyable and challenging for everyone.