in brief,
Bitcoin will only be a digital currency that help people to do something,
it will never can be a fiat because we need to think about its physical form,total supply and many others.
crisis will happen if we're forcing it and replacing our own fiat with it because some people hold a lot of Bitcoins in their pocket.
Digital currency is a nice thing, maybe in the future, a global currency will exist based on Blockchain that will go mainstream and all fiat will not be needed anymore. We are at the pace of innovation and many things and technology will be invented in later years. The world will be different in a digital way where physical form will not be needed anymore. As to the total supply, maybe the world will agree on dividing the the total supply based on the countries wealth. It'll be hard but who knows, maybe in the future all leaders will come to a point where there will be no more wars. It's just an opinion and purely speculations.