While this is not a feature that is high on my priority list, and there are a few threads already in existence discussing the possibility, Yoshi-P states here that he will consider adding a single server dedicated to open world PvP if the players express enough interest (right at the 8 min mark). I figured that it would be a good idea to centralize the discussion around the point that he mentioned in the video in a single thread.

So, for those who would like to petition for at least one server offering open world PvP, like this post to let the devs know you are interested.