I dont see it ever happening, to be honest. Why invest the time in building a wrestler up as a future star, only to have him lose as a result? The winner has the opportunity to wrestle the champion anytime, anywhere within the year following. It would be terrible booking for the wrestler to be booked to just face the champion in a one on one match, or a 5 way match(like Hernandez did in TNA), or have him cash in on the champion after the match, only to lose.
Money in the Bank is supposed to be about elevating wrestlers. Edge's win may have been a transitional championship reign, but he went on to win ten more. RVD won his first major title and would have been the face of ECW had he not been busted with weed. CM Punk was elevated to main event material and to one of the top heels in the company. Jack Swagger, well hey, you can't win em all. Kane used the briefcase to kick off his first major title reign in ten years, and one of the most compelling storylines of 2010. And Miz' win marked the beginning of a reign that would see him win the main event of Wrestlemania.
A win of the MITB contract and a loss thereafter would be a deathblow to a wrestler's career. The MITB match itself is about making someone into a huge star. With the field up to 8, thats even moreso the case then ever before. It's a grueling, brutal match, and the winner, be they heel or face, has always earned the victory by proving they can take a pounding. For them to then cash in and lose would not only be a large blow to the wrestler's career, especially an up-and-comer, but it would be non-sensical that they beat 7 men but couldn't beat a weakened champion. Im not even going to try and speculate, because it would be incredibly dumb booking and I dont think its something WWE would ever do. Unless, of course, they want to bury someone's career.