That might be a step forward, but the problem with this is that it will under-lend to things that are societally valuable but not personally lucrative.

For example, we want lots of teachers and librarians, social workers and nurses. But if we only pay based on personal income, we'll get lots of people with low social value but high income. E.g., corporate lawyers, investment bankers, corporate raiders, advertising executives.

I think the better thing to do is publicly fund education and the have the government capture the gains via taxation. That's harder to tune, but I don't have reason to believe the outcome will be more lopsided than a purely market-driven approach, and has the big advantage of not funding a whole industry of student lenders.