People who supported bitcoin are just too happy with what they are seeing, bitcoin's value is increasing and yet they think already that it will replace dollar. A realistic person would not think that way because it will never happen that a legal currency will be replace by an anonymous or decentralized one
As the wisdom says, never say never
We have by now seen quite a few spectacular crashes of fiat currencies. The German mark in the Weimar republic and the Zimbabwean dollar in the country of the same name are likely the most known and conspicuous examples of fiat currency complete collapse and fiasco. But there were a lot of other such downfalls which didn't get wide publicity. As a rule of thumb, when a state crashes, its currency crashes together with it. In the Weimar republic, the government had to effectively return to gold standard. Robert Mugabe, the Zimbabwean decrepit president since 1987, had to accept as Zimbabwean official currency (in fact, a number of official currencies) what regular people had been using by then instead of the completely devalued Zimbabwean dollar, i.e. the American dollar as well as a couple of other currencies. Therefore, if something similar is going to happen again in the future, Bitcoin may well become one such currency, especially if it gets wide traction between local people by that time