Here is something that I would really love to see implemented in the game:
An independent PK area, similar to the Doppelforest in my favourite game ever - Talesweaver. I hope you guys have heard about it, if not you definitely missed something out.
The PK area is a place where anyone can enter anytime and fight against anyone who may already be there. Its basically a Free For All fighting arena. If you enter as a team, you obviously fight as a team. It would be loads of fun to have PVP outside the rather stiff arena battles.
To spice things up a bit these areas could also contain mobs, which were called “Doppels” in Talesweaver. They are mirror images of actually playable characters who can also use a limited amount of skills and have incredibly high HP. They would drop the rarest of rares so of course you would go in and hunt them with your friends but alas!, there comes another party on their hunt for Doppel-Rares and now you are facing not only one, but two foes.
In addition to the Doppels there might also be other boss monsters with nice drops, as for example the Kunohen in Talesweaver. I would really love to have a Kunohen in ToS, too. 
But I am getting carried away…
So basically I suggest adding a FFA PK area (maybe seperated for every 50 lvls), with Doppelganger mobs and boss monsters… Would be awesome innit?
I even found a video of Talesweaver PVP:
And a picture of a low lvl party trying to fight the Kunohen:
have fun!