Why does he even think like that in first place. It is the price difference and exchange capability of bitcoin and fiat currency which us making is rich. If that gets replaced with one currency then how we can get the profits or how we can differentiate ourselves with that price tag. I think it's not possible because it's just not well possible! There can not be two sun in the single solar system, it will burn the life. So there can not be two currency otherwise it will just break down the economy of country. The dollar bill is something related to traditions, old ways of trading and it will never get replaced in any time soon. Bitcoin is perfect fit in the internet world and might not just fit in the real world. So may be not this time.
While I do agree that two currencies cannot be the main currency of a country, I don't really agree that the world is all about tradition. The traditional way might be sending money with dollars. The traditional way might even be physical fiat but that's clearly not the case anymore. In this modern age, people don't really embrace traditions that much anymore. People seek something new everyday and bitcoin is something new. It's only a matter of time before bitcoin gets considered as a "cool" thing and people will follow the trend. These days, people are into bitcoin because of the ridiculous gains it had given us in the past couple of months.
Another thing, I do agree that bitcoin cannot be the main currency of a country together with their local currency because bitcoin is not taxable. The country will have no funds and so they will be forced to ban bitcoins (which is quite hard to do, impossible even) or put a huge percentage of tax for fiat currency users, which will then of course force them to use bitcoins instead.
