I would view that as a horrible compromise, because it would result in poor people receiving worse health care than wealthy people.
Additionally, we already had that system in place, it was called "lifetime limits" and it was typically $1-2m on the best healthcare plans.
It's impossible for that not to be the case. It's even the case in countries with single payer, because rich people who live there and don't want to wait for an appointment or want something that isn't covered will just go to a country that can give them what they want and open their wallet. Even without leaving the country, they can hire private nurses and so on when they aren't covered by the national health system.
Moreover, why is this supposed to be a problem? "Money buys things" is the purpose of money.
There are things a rational national health system wouldn't pay for because they aren't economical, but a rich person would buy for themselves for much the same reasons they buy a Tesla instead of a Dodge. Which means they have a safer car because they have more money. Should we prohibit expensive safer cars because poor people can't afford them?
Ie: I broke my toe and I have insurance, so I get ER treatment, but that guy who has no insurance and is internally bleeding to death from a street stabbing (and is hispanic, doesn't have insurance and maybe isn't american?) is pushed behind me in line. That is the real life scenario that at least one person is advocating here.
I think as the governments become more starved (not made more efficient by reducing costs, starved by simply cutting funding without optimizing it logically) that important government services will have to replaced with tiered private companies. As regulations are removed, the same thing occurs.
What if a speed of ambulance was built into your insurance? How do you know what response time is right for you and your family (as it will be framed)?