I agree that China isn't close to surpassing us in the near future. Notice I said in the next few decades. In the short-run, I think China is about to face a massive depression. However, both China and India are making the move toward free market capitalism and growing by leaps and bounds. In 50 or so years, the balance of power will shift toward them.
It's simply a matter of population. China needs 1/3rd the GDP per capita of the US in order to have the same total GDP we do.
If the US wants to stay on top, it needs to encourage more people to move here.
Besides, encouraging the migration of cheap labor, academics, scientists, entrepreneurs, businessmen, and others will do nothing but benefit the United States.