A villager extortion mod would be funny. Add in the capability to run a protection racket on town merchants and you're in business. You can already charge a toll to caravans, why not a "Give me money or I'll burn your store down" fee? 
While we're on that, a kidnapping mod! Kidnap the girl and ransom her back to the town. Then the local hero meets you at the village and gives you money.
There is so many idea that come from the *quest*, I.E.: The ability to train your troops in the trainning field maybe? like when yu train the peasant! you against a certain number of troop you choose and you have to knock them out like the peasant.
Ability to force a lord to turn against his king for a set number of time by kidnaping his girl, since he doesnt have the choice the king wouldnt be upset.
Ability to send spy to destroy food stocks in a town\castle.
Send a messager to buy stuff for you in town ( when he reach the town the trade window appear so you can choose what to buy then he come back ) ( could get ambushed pursued killed by ennemy lord looter raider etc.
When you get friendship to 99 with a lord a chance to turn him to fight for you against his king or simply make him join you and protect your fiefs.
Pay a blacksmith to make a certain kind of item for you and it take time and cost a bit more since its aspecial order ( To hell finding a bunch of 10 Heraldic mail with tabbard for those that follow you and finding well 10 of each of what you need to make a nice companion army

)
Possibility to pay blacksmith to upgrade weapon\armor
and so on and so on.