Good luck with your hunt for open world PvP, I hope you can find it. As others have said, the PvP focus in WoW has shifted over the years to smaller Battlegrounds and arena matches. From what I can tell, it looks like the expansion might be bringing in a PvP zone in the form or Tol Barad, but I havn'e tchecked it out in the beta myself.
The way gear and levels scale in WoW means that any level 80 can destroy anyone who's lower than 70 in 1-shot. Although the old world is quiter now than it used to be, I expect the expansion will bring the top level players and those who are still leveling up into closer contact - it may well increase the amount of world pvp going on.
If you are still hankering after the open world pvp aspect, and want to stick with wow (over other games) you could always go to the PvP forums and start a thread - ask if anyone knows of a server wher open world PvP still carries on regularly - you might get lucky and find all the open world PvPers on the same realm