I would not say the US is absolutely massive, just add up the Euro nations who have State Funded Healthcare and compare the populations, and you will not be far out, and that is across entire nations, differant languages and all.
Its not the size of the population that is all that important, if anything a large population would bring economies of scale.
The issue for the US is that you do not have anything like universal coverage, and yet as a percentage of GDP is actually costs more than here in the UK.
The issue really is at what stage is the healthcare system funded, for the UK it is free at point of use, but then it costs through taxation, for the US, its a mixture depending upon a number of factors.
The one benefit we do have over here, is that folk do not tend to go bankrupt due to healthcare costs, however its also true that insured US citizens can expect to be treated for conditions that are, well for want of a better word, rationed.
We in the UK can buy medical insurance, just as the US, but only a few are motivated to do that, because they have to pay direct from their own pocket, and few companies offer medical insurance as part of their employment terms.
I think that perhaps there is the possibility of state insured medical care with private providers as a model the US might consider.
You choose who your provider will be and change if you do not like the service, and the funding moves around with the patient.
Individuals could then supplement the state insurance if they want to go to more expensive providers, in other words you could choose the amount of health based taxation you pay.
There would be some problems as you’d get towns where there was effectively only one healthcare provider, which would be pretty much a monopoly and no doubt you would get healthcare provider companies who would buy out competitors, so I would expect there to be some form of market regulation.
A system where the healthcare provider could go bankrupt, along with some anti-trust legislation might help keep the system getting the bloated administration and support that many hospitals in the UK have.
I think the most important thing though, is to keep healthcare out of the political realm of influence, because meddling by politicians is a sure way to screw the whole thing up, this we understand all too well in the UK.