This is where I think, then, you'd need to think about, first off, whether this is something voluntary or mandatory. If you think about employed workers, they don't have an option. They are required to pay in.
The second thing is, really, to think about how you would assess their incomes. The thing is that someone who is a paid worker is receiving a regular paycheque, whether that's weekly or biweekly. There's a clear record of what they're receiving. The challenge, then, with self-employed and gig workers is that this may not be the case. The timing of their incomes can also vary. Sometimes they could be working consistently yet only receive a paycheque—I guess I should I say “income” or “revenue”—once a month or once every, let's say, four months.
Think about a real estate agent, for example. If you get a number of sales, you might get quite a bit of income at once. If you don't, there could be several months between receiving revenue. There's a great diversity among self-employed workers and gig workers. That's where some of the challenge comes from.