I think it would "fit" the FF14 world to hit accept for a duel or party vs. party request. In doing so, the screen would have a cool transition to a battlefield-instance where everyone fights.
(Even better if you could somehow choose which battlefield to go to)

Basically, to keep some FF-flavor going on, the screen transition to the field would have a great feeling. At the end the winner would hear the victory fanfare and be rewarded something to make it worthwhile (credits or PvP points of some sort perhaps).

What are your thoughts?