I think having a dueling system would be awesome! I miss not being able to fight your friends whenever and where ever. Does anyone know if they will be adding any type of dueling system?
I don't think they have completely ruled it out, but there are no plans that I know of to add it to the game anytime soon.
In general, ZOS seems to be reluctant to add any form of PVP that would take away from the AvAvA in Cyrodiil (e.g. arenas, battlegrounds, etc.). You can never say never though.