I consider it more likely that the USA goes the way of the USSR than the possibility that they could pull that kind of a rabbit out of their hat.
I can't see it either. They would be building a proven failed layer on top of a proven successful system. It would basically be a centralized side chain controlled by the US government. I don't see how people would be incentivized to use that when they can use a decentralized solution... maybe not bitcoin directly but a decentralized side chain of sorts. Perhaps people would still use a government sponsored currency because government would provide insurance (FDIC) against theft and loss, but private insurance solutions can work just as good or better for that. However, government always seems to find a way to maintain control but I believe their power will be weakened, and there may be a certain segment of the population that will always choose to use a government sponsored currency.