The Arena is here to stay, but PKing is no longer limited to that instance. "PK anytime, anywhere" is the motto used in ToF now, so watch your back as you travel through Elterra. One-on-one battle is great, but if your tastes run to something on a larger scale, try Inter-Faction Wars. This massive free-for-all PvP area is open for two hours daily, with every enemy kill earning you Honor Points that you can trade to NPCs for better gear.
The new PvP system is live now, so check out the Tales of Fantasy site for all the details, and good luck!