It's even delusional for anyone to think that Bitcoin is going to replace the fiat system, when the purpose was not that from the onset; rather, Bitcoin was created to give people a choice not to depend only on the fiat system. You can't completely survive in a country as a citizen without using fiat unless you don't want to deal with tax, and the government can't even permit such to happen.
Those are the people that consume much of John McAfee content who is so vocal about the death of the US dollar and the supremacy of bitcoin, something he does to keep himself happy and relevant. It is good to be so hyped about bitcoin but giving bitcoin unrealistic attributes will not in anyway make it to become or do what it is not meant to do. Bitcoin was created to exist alongside the other fiats, there is no way nations will jettison their currencies for bitcoin.