I'm not exactly sure. These programs are still in there trial phase anyway.

The one program that I looked into had a relatively low cap on it, like $60,000, so they only take a cut of the first 60k. Plus the majority of people (i.e., outside of engineering) don't get equity anyway.

Couldn't you just use income reported to the IRS? Then any odd payment scheme to get around repayment terms would necessarily be tax evasion, which is much more serious and lets you lean on the IRS for enforcement and legislation.

Many forms of what you call "tax evasion" are in fact legal in the US.

Lots of very, very wealthy people have no "income" at all, which means they don't pay taxes.

The problem is that "income" is narrowly defined (for a reason) so things like someone owning a large corporation which triples in value over a year making them a billionaire on paper don't even show up on taxes because officially that person hasn't "made" that money until they sell the corporation. Even when they do, it's taxed at a lower rate than "income" because it's a different "kind" of money.

Couldn't they just look at Adjusted Gross Income?

It's based off salary, not equity.