Australia has an interesting system, the government owns the student debt and once you earn above a certain amount it raises your tax rate slightly until the debt is paid off.

Those who can earn enough money eventually pay it off, but they're not worried about debt collectors if they're not earning any money.

People who don't ever earn enough simply don't pay it off and it's not a problem.

To prevent abuse from the universities raising costs too much, if they want to participate they have to adhere to set rates for degrees. There are a couple of universities that don't participate in the system but they're no-ones first choice