I really believe adopting a pvp system similar to Ultima online would fit perfectly into the game with how cities are set up and having a few major cities, adopting a faction system for example: 1st faction: Ardholm 2nd faction: silverlake? 3rd faction: erdvine.
each faction would be joinable and once in you can play normally like join guilds etc. your leystone then could teleport you to your factions city instead of just any, or maybe get a faction specific leystone so we could have two?
each faction would have a reputation that each player contributes to so that means if you go out as ardholmiens(lol) and slaugter a bunch of erdvininites(nice) you would get negative rep and could potentially become at war, which results in all out pvp anywhere. You as a faction could repair this reputation by maybe having a faction chest that they could donate supplies like crafting etc to and said chest could also be robbed.
I think its a very nice system and could bring in really interesting gameplay, or maybe its not the right fit let who knows