This is how the HECS system in Australia works. It's not novel. It's simple and straightforward.
The government pays for your university tuition and then you pay additional tax each year that you're employed post degree. Interest is charged at CPI so there's no blowing out of the debt if you struggle to find work immediately / spend time in low income occupations. Most people pay it back within 10 years, so you're debt free by your early 30s.
The government funding this system = equal opportunity for entering university = more skilled workers = more tax for the government in the long run through the higher incomes that university educated people earn.
The % of your income that is garnished each year depends on your earning capacity:
Below $51,957 = Nil
$51,957 – $57,729 = 2.0%
$57,730 – $64,306 = 4.0%
$64,307 – $70,881 = 4.5%
$70,882 – $74,607 = 5.0%
$74,608 – $80,197 = 5.5%
$80,198 – $86,855 = 6.0%
$86,856 – $91,425 = 6.5%
$91,426 – $100,613 = 7.0%
$100,614 – $107,213 = 7.5%
$107,214 and above = 8.0%