Third World contributions to First World living standards

They would improve.

A change in labour rates would be far offset by the fact that Americans would suddenly have billions more consumers ready to use American products. The same would be true of everyone; the entire world would be much richer.

Competitive advantage isn’t comparative advantage. Someone would make affordable iPods. What the price would be you can’t say for sure, but if they’re, say, $600 in this amazing new world, nobody will care if their income triples - which is something it might if everyone else in the world was as rich as we are now.