To me this is like harmonizing mail and e-mail. It's not a one-to-one swap or replacement, although that is the overall intention. The technology will be phased in or out respectively based on advances in infrastructure. ie we will likely always require notaries to some degree so that we have witnesses to testify if documents are called into question in a court proceeding. This doesn't have anything to do with mail or our need for a mail system. So contrasting, the day we are past the tipping point on device-based payments, there will no longer be a need for payment cards.
It is not as simple, you could say this happened with fiat and electronic fiat, now most money around the world does not have physical form and instead are just numbers in a computer and there are even some countries that are thinking about disappearing their cash, but this is different, cryptocurrencies are not fiat, there is nothing backing them that is true but there is not government either telling us that it has value, it is entirely a new concept.
And governments understand this very well, they are not going to accept cryptocurrencies that easily because they know that if they do, they put at risk the system they have built and in which they are so comfortable and they are not going to lose everything just because someone created something revolutionary.