Losing items in duels has been suggested before. It was a horrible idea then and it's a horrible idea now.
i think all of the workers will say "bad idea" and the others will say "nice idea"
A competent, active dueler can easily have well over 100 losses. I completely disagree from all standpoints: builder, non-combatant adventurer, dueling adventurer, dueling worker, dueling soldier.
I'll add that it would be easily exploitable to transfer items to other players.
Edit:
Unless I'm misunderstanding you and you don't mean stealing items but just getting items from out of nowhere like regular jobs, in which case it's not absolutely horrible, but I still don't like it. Celxius claims there's a parallel, but that's not entirely true. The cash comes directly from the other player, as does the danger. The only way to make a parallel is to steal items, which would again make the idea horrible.