Simplest way to implement it would be duty-style. After agreeing to the duel, both players would have 45sec or w/e to hit Commence, then get teleported to a small instanced arena. Rest as in Feast/Frontlines, waiting to start, change your PvP stuff, etc.

Now if you also wanted an audience to watch your duel... well that's a different question entirely. Not sure if spectators are in this game anywhere. Spectators would be another step towards "essential PvP features"