I've thought of this idea before, but what really worries me is not drama, but how would you prevent leeching here?
Sure, kill people around your level to grind, kill those even higher level to gain more exp. But... unlike pvm, here your "opponent" could be just a friend (or bored) and will just sit there waiting for you to kill him for easy exp. Worse, what if somebody just sets up a "dummy", high level character which everyone is welcomed to leech from by killing it?
Earning exp when killing another player is pretty easy (nay, even trivial) to add, but how do make sure the exp is justified and the character actually earned it? (rather than, say, two characters who just ctrl+click each other all the way to L99?)