I can imagine a simple model where a customer requests a ride. The nearest 3 drivers get asked how much they want to take the fare (perhaps a simple UI saying "What would Bob have to pay you to get a ride to Brooklyn? [$12] [$15] [$20]"). Driver who offers the lowest gets the job.
Uber sets the middle choice to be their guess of the market rate, and the above and below options allow the driver to either undercut to be sure of getting the business, or raise prices to try and get more money.
Considering how much Uber is under pressure for employee vs contractor and unionisation, I'm surprised they don't do this.
