And anyways, it's still in your best interest to pay it off as soon as possible as most of the debt will be at 6.8% interest or higher.
Based on this new change that could easily not be true!
Keep the payments at 15% and it will easily be true. And even otherwise, you are taking on even more of a risk by playing the bond market, with the chance that the program could be changed in the future. Especially the people who get helped here due to their finances, they can't afford to take even more of a risk.
I don't even know anyone who would do that. Sure, people familiar with the markets might, but I doubt they will be making 40-50k for the next 20 years. Also keep in mind inflation, 40-50k probably will be a very meager salary in 10-15 years. So even those stuck in low paying jobs will be making that within the next decade or two.