To me, radical has nothing to do with if it's done somewhere else or not. It's if it's a drastic change from what we currently have. A $15/ hr minimum wage nationally would be a drastic increase from what we currently have. Sure, there's spots in the country that have that. But, as a "norm" across the country, we don't. Medicare for all is a radical change from what we currently have even though other countries have it. It would be a radical change from what Americans are used to and have experienced.
Now, saying that, I'm not against looking at what I consider radical ideas. I've been pretty vocal on here when discussing healthcare that I'm all for an honest discussion looking into single payer plans for the US. I'm not for an across the board $15 per hour minimum wage in the US. If some municipalities like Seattle or Los Angles where living expenses are outrageous want it...great. I don't think it's needed in rural America where living is much less expensive. I would prefer to look at the increase in taxes on the upper income levels first. See how that affects income distribution and go from there. Saying that, I'm would be much more for it if it were say around 50% instead of 70%+.
So....just because something is "radical" from what we currently have, doesn't mean it's not worth discussing.