However, I have yet to read/learn of a system that would generate both the cutting edge medical wonders available in the US health system (for all its flaws) while truly achieving universal coverage.
"Medicare for All" is a neat slogan, but to actually achieve single-payer care and universal coverage would require several layers of brand new institutions and years of graduated transition. If people complained that the ACA bill was very long or complex, then the bill ushering in the new system would be at least an order of magnitude more so. What needs to happen is for Congress to establish a commission to return with some plans in 2 or 3 or 5 years. Of course, who's to say that future government or the People have the patience or commitment to follow through once the time comes? So if it comes, it comes haphazardly. That's the 'democracy tax'.

2 Coverage via the workplace came about in the USA through Union contract efforts to improve the lot of their employees (since an organization negotiating for 150k people has more cost control leverage than the individual,3 and through organizations adding such 'fringe benefits' as a feature to draw in better employees for their organizations. Government then used this model to force all employers to do this, undercutting organizations' ability to use it to acquire the services of a higher caliber of employee and putting all of the administrative burden on the organizations AND loaded it up with government mandated minimum requirements that have driven up the costs. How well those higher costs have accomplished improving overall health coverage nationally is debatable as Senator Sanders recent Presidential bid suggests.
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Government expansion via workplace coverage was a compromise, and workplace coverage only emerged in the first place because healthcare and health insurance as we know it did not yet exist. Today the product and service that needs to be provisioned is totally different, and we need to change how we do it once again. As with adaptation to climate change, the thing that wants central administration has to be transformed because it is no longer sustainable in its present state under any administration. This is two problems at once, economic and metaeconomic, and they're inseparable. We can't and shouldn't expect a mere reduplication of current practices with a different set of paperwork.

3This economy of scale concept is often touted by those in favor of universal healthcare. However, when only one consumer exists, the normal functions of the open market cease to operate. If there is an economy of scale at that level, it simply does not conform to the normal model of comparative negotiation in market interplay.
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This is an important point that follows from what I said about metaeconomics and sustainability. Even with a single-payer paragon established in the United States soon enough new crises in quality and absolute costs will emerge that can only be addressed by transnational governance of healthcare -and probably more. But, one step at a time.

Far too many of the national systems feature people flying off for faster medical treatment elsewhere or "black market" medical practices etc. cropping up alongside the official system.
I think these "medical tourists" to America can be generalized as economic elites, with a small proportion of non-elites being sponsored for experimental treatments or purposes of research into rare conditions. There is medical tourism out of the United States as well, but the profile is inverted: those are lower or middle-class people who cannot afford treatment locally.