How should we gauge the feasibility of Medicare For All? Should we look at similar policies that have existed for decades in other countries, at Medicare itself, or at a change in how ride shares are handled at this one airport? Really, who's to say.
Back in the late Bush years some respectable-ish libertarian econ blogger challenged left-liberals to say how efficient they thought a government-run health sector would be, on a scale of one to ten, with ten being the paperclip industry (super cheap, easily available, consistent and predictable quality). I don't think he ever said what number he would have given the health care industry as it already existed.