First, to start, I am the type that most likely would not participate in PvP at all unless it is with friends or a guild event.
I believe that SoE will most likely add PvP later in the game, either with seperate servers, an arena type thing, or duels. For those that say PvP cannot work with the current story, I can definitely see it working in the future. Right now the cities are expanding their own influence, carving out their own places in the world. As the number of people in each city grows, and they become more powerful, their reach extends further. Eventually they will collide, and they will run out of feasible places to expand to.
I could definitely see a PvP system where outposts are taken and conflicting sides fight over these outposts to expand their influence across the realms. However, I don't believe that they would fight just for the sake of fighting (I'm good, you're evil, die scum! just doesn't make much sense to me).