In the online arena, you could choose to watch and bet on these fights, people voting for the winner would split the total amount of gold collected in the pot. When you chose to fight, you could enter the fight under your gamertag, instead of the default names such as "The Butcher" or the "Black Arrow".
The two combatants could also fight to collect the other's helmet or hood used during that fight. The loser should not have to lose his helmet completely, the winner should just get like a duplicate saying "Sneakyness' Hide Helmet". This would make a cool kind of trophy case that would add on to this DLC and it would also stop "boosting" because the helmet/hood would go into your trophy case.
But yeah, its just something I'd like to see in a game and I think a lot of people would agree. Plus, you would satisfy those who wanted multiplayer in the game and wouldn't have to take away or add on to the main storyline at all.
If anyone wants to discuss or trade opinions on Skyrim, feel free to add me on XboxLive, my gamertag is Sneakyness.