The issue is, the IFRS is used by THE WHOLE WORLD except the US. It's kinda hard to convince everyone on the world they are wrong except the US. So eliminating the IFRS and incorporating the GAAP worldwide ain't gonna happen.
As for the opposite, the US is the biggest economy in the world. In such a huge scale, even the smallest of changes cause ripples that affect all economies in the world. Trying to completely change their standards would probably crash not only the US, but the whole world and lead us back to the stone-age.
The US economy can't be changed cause the world depends on the US, and the world can't be changed cause it's just too big. So both systems will forever co-exist.