Hopefully it's similar to UO where the arenas and dangerous terrain are always there and available but there just isn't always something going on. This means you can go to the city arena for mutual combat at any time of day but there may or may not be an official gladiator match going on. If there is you enter it. If there isn't you walk around challenging people with a sneer and a boisterous attitude.
I didn't like the arena idea much, very restrictive. I liked the open world where bad real players can come by anytime. And I'm sure that's what a lot of people liked as well.
Since the game isn't an mmo, but rather a multiplayer/singleplayer game, it would be neat to see something like Dark Souls' invasion system where a player could enter into another (randomly selected to prevent griefing?) person's game world to try to kill and loot whatever they can.
I have not yet understand exactly how this multi/singel setup works. But i would love to see open World PvP as i knew it in UO where you could encounter a PK when you transported your valuables and risked to die and get looted. Or being the PK yourself. Or chalenge Groups of pvpers out in the real World where you could use the suroundings to win the fights
