Here is an example of the potential cost.
Borrow $250K for a 4 year degree. Be single, and take a job where your after-tax net is $50K. Your poverty line is $10K. You have $40K to target, so your 10% payment is $4K, for 20 years. That's $80K in total payments. That's taxpayers eating $170K of principal on your education choices. The inflation of your income would be offset by no calculation for interest.
Under the prior plan, which was also part of the problem, the above example would be $6k paid per year for 25 years, or $150K, and the taxpayers eat $100K, not $170 K.
The new plan took a moral hazard, which has been a big part of this education inflation bubble, and made it worse. Obama moved it up two years to buy votes. And made it worse again.