I do not think that will be possible in this century. Because people who want to use bitcoin, they must at least understand about technology and the internet. But now there are still many people who have not understood and can not use technology and internet that exist today. They can only do their daily activities with physical money. Indeed everything can happen. But it will take a very long time and it takes the emphasis of technological education to people who do not yet understand. If all humans in this world can already use technology and the internet, it may be physical money will be replaced by digital money.