#Medicare4All is not part of the DNC's platform, so adopting this issue in the Libertarian Party's positions wouldn't make the party more like the Democratic Party on this one issue. It is popular with democratic voters, but what evidence is there that the DNC listens to it's base?
#Medicare4All lowers government costs in all countries that adopt it, so I'm not sure it is an automatic fail for libertarians, but probably wouldn't be popular to the funders of the Libertarian Party, the Koch's. Our current medical system uses the ever expanding government to favor the medical industries and give them handouts, which isn't conducive to free enterprise and competition.