There are also some private organization who doing something similar. Where essentially they are encouraging people who fund scholarships to fund after graduation loan repayments instead where the goal remains for someone's student loan payments to not exceed a certin % of gross income. I think in those cases they are operating in an insurance model, where the insurance premium is paid instead of a scholarship.
This idea is already being tested in Oregon state schools, though it has been a while since I heard anything about it's effectiveness. (http://www.huffingtonpost.com/2013/07/16/oregon-free-college-plan_n_3606990.html) I think it has only been an option for a couple of years (if it is still something they are pursuing). It's a great idea in theory, because it also frees students who want to pursue less lucrative fields like teaching and social work to do that, because they functionally pay less than IT and business graduates. But interest doesn't magically disappear when you move funds from loans to deferred taxation. Time value of money is something public budgets also have to consider.