That's the worst of both worlds approach. Nobody is happy with how ERs are financed. Not free market conservatives, not government intervention liberals, not the doctors, and not the patients. The only people who like ER's cost structure are insurance companies, because they only pay for healthy people who don't cost money and pass the buck to the government on sick, poor, and old people.
Extending your analogy, if we took the ER model to firefighting, rich neighborhoods would be hugely profitable and have plenty of fire fighters (because they're willing to pay and don't burn very often) and poor neighborhoods would either burn or be covered by government subsidies, meaning the rich people pay for fire service twice, once directly (for which they get very little) and a second time through taxes to subsidize the poor (for which they get nothing). Everyone would be better off if everyone paid into the same pool, since now the fire companies aren't taking a cut off the top for the minimal service they deliver to the rich, while not reinvesting for coverage to the poor - because there's nothing in it there for them.