Solution to student debt? Pay no tuition upfront, but pay back part of your income later

The average college student graduates with around $22,000 in debt. But what if you paid nothing up front, and then were required to pay the school back when you get a job? This idea has gotten backing from various venture capitalists. Purdue University is trying the approach along with an online learning startup called Lambda, which wants students to repay 17 percent of their income if they find a job earning at least $50,000/year.