As a Canadian in the US to me this feels like a different kind of horror show. I play bridge and as a result I've been exposed to quite a lot of the elderly dying as a result of chronic conditions given the demographics of the game/sport. In Canada, it seemed we had a charity fundraiser 2-3 times a year for someone affected by some condition the government didn't want to cover due to cost. In the US, I deal with a level of convolution that might make the Byzantines envious but have a sense that the best plan on offer covers far far more than the rationed system in Canada. I think the Canadian system nets ahead on efficiency, but I'll quite readily admit that efficiency has some rather nasty tradeoffs.
There's certainly a discussion to be had on what level of care should be provided, how to pay for it, and what to do when the care required isn't provided.
I don't hear a lot of complaints about medicare not covering important things (but I only have limited exposure to that), and I assume a US single payer system would essentially be Medicare for all. I do hear complaints about Medicare not paying providers enough, and a lack of available providers.
A rational method of rationing care seems preferable to the current byzantine methods. My (likely naive) hope would be that spending the same amount of money on healthcare, but with fewer parties involved would provide more and better healthcare. At least we haven't reached the point where the government encourages smoking to decrease long term healthcare costs.
Remember how proponents of single payer like to point out that US government healthcare spending per capita is higher than many countries with single payer, even though it only covers part of the population? That's probably related.