This looks like a crude version of socialised healthcare to me. Other socialised healthcare systems around the world should in theory face the same problem, wouldn't they? But AFAIK they do not nearly have the same cost issues as the US, at least I'm not aware of this here in Germany.
One theory I've heard that sounds plausible is that
a) insurers do not pay anywhere near what hospitals bill to uncovered patients
b) hospitals do not even expect patients to pay the whole bill, but more like 20% of it, so it is always good to contest the bill
So the problem is that hospitals are cash-strapped for systemic reasons, but can't get it from insurers or the state because those have contracts in place. So hospitals try to squeeze uninsured patients as much as they can with inflated bills, with predictably horrifying consequences. Insurers don't mind because that makes the case for buying insurance even stronger.
So one solution might be to pay for poor/homeless care via state/federal budgets. This could cover poor people up to an income level that can afford insurance.