That's generally Lambda School's model - we train people to be software engineers for no upfront tuition in exchange for a share of future income for two years. We also have experiments running with housing and living stipends in exchange for a share of future income for three years.

However, I consider recommending that to someone who is homeless and/or destitute exploitative. I can't put my finger on why, but knowing how desperate you can feel in that scenario I don't feel OK turning that into a money-making (or even transactional) scenario.

We've found that the folks who are hired and now-housed tend to donate enough to keep the fund alive once they're on their feet, but I don't feel right requiring it.