I suppose any issues *can* be solved, I just think most of the issues with Medicare for All won't be solved. At least with the ACA it was an extension of the current system, so it was far more easily implementable. I think the Republicans only hate it because it was led by the Democrats, and personally I think they're damned fools for hating it so much, because the alternative, single-payer, is worse for the insurance and healthcare industries.
The ACA (Obamacare) wasn't in place long enough to judge it properly. And since the Republicans gutted it by removing the mandatory coverage provision, we'll probably never know. Personally, I hated the ACA, because it cost me many thousands of dollars in extra taxes, which the Republicans have conveniently kept in place, damn them.
And, again, I think the EU and Europe is a bad example for the US in pretty much every way.