Firstly, becoming a town guard. I'd love to officially join the few, the proud, the town guardsmen. I thought of it as I became a Thane the other day and thought, being a Thane dosn't suit my character but I would love to be able to sign up as a town guard, busting up criminal scum, skooma busts, arresting drunken brawlers and lowlifes, all that jazz. It would be such a cool way to pay the bills so to speak, instead of chopping wood and picking vegetables and stuff. Perhaps you get paid based on how many crimes you stop or bandits you bring to justice?
Another notion I had after this thought was, how kick ass would it be to take on the thieves guild and all the other criminal scum in Riften? Perhaps you and Mjoll meet up in the tavern in the corner to discuss bringing an end to the criminals in this rotten city and begin a descent into corruption, intrigue and danger as you investigate and take down all the criminal organizations in the city like the thieves guild, the Black Briars and maybe the corrupt guards.
Maybe you start the quest after becoming a town guard and fight your way through corruption within the system?
I just feel like this needs to be in the game. I'd pay money for it.