Bitcoin is digital currency and also one of the commodity like gold. It cannot be replaced with USD, still major countries are not still not accepting bitcoin as one of their option. It will take lot of time to establish a digital currency into physical one.
You mean it'll take a lot of time to replace physical with digital. It will not, because we're getting used to it right now. We have seen how easy it is to complete transactions online and how useful they are. The world is changing at this moment.