I think it is a futile exercise to attempt more than the broadest of projections when dealing with a time horizon of two or three decades. With that said, I too would bet against China becoming a larger economy than the United States within the next twenty years.
Right-wing fantasy. Dude, the US already has absurdly, dangerously low tax rates - they can't go any lower without complete collapse and chaos.
We have a spending problem, not a taxation problem. We need to cut spending, not hike taxes.
Here is a good bet: The Romney Administration will alleviate the spending problem while helping to boost consumer/investor confidence to pick up the slack in the short-run.