My suggestion is, implement 1v1 or duel in the open world of Tyria. Players can easily request duels anywhere except in towns or other places not suitable. Possibly, players can have the ability to switch to pvp active or non-active at all times, except during a duel. This way, players who have switched to pvp active can see which other closest players who also are active for pvp. Players ready for combat 1v1, pvp active, can have fun while others not active will be uninterrupted.
I can’t see why this would be a problem anyhow.