Add a new Faction and area that focuses on PvP.
Maybe add a PvP Ladder and a dedicated arena for those who want to fight formal 1v1s, 2v2s, or free-for-alls.
Getting player kills or Ladder Ranks give you a new item which you can use to buy PvP Faction exclusive items.
i.e.
Faction: Bloodsworn
- Invading and killing other Players in PvP Rooms.
- Reach higher ranks in the Ladder.
- Winning in the arena.