The U.S. may no longer dominate but with 300 million people and tremendous resources we're not heading to the bottom of the heap either. Our standard of living is going to move back closer in line with the rest of the world, which is fine.
I'll accept 1 American moving from upper middle class to lower middle class if it lifts 3 people out of poverty in the third world.
In some ways, this makes me long-view bullish as an entrepreneur. Imagine the opportunities to serve a global market that lives at first world standards.