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.
yeah bitcoin is digital currency and you are right that bitcoin is still not acceptable in some countries but i hope bitcoin will be sooner acceptable in everywhere in all world in the near future and i am sure bitcoin can be appear in physical shape in few years .