By then, your question should have an obvious answer.
Well if he will be right, then we are all fucked up. The tax will now come to bitcoin and we will have a lot of problems regarding that. If people are ready to accept bitcoin as their currency then are we as bitcoin users ready to be taxed? It is now the other way around problem.
It is obvious he is just trolling. That or he is living in a different dimension. Governments will never get rid of fiat. It is a representation of them and how rich their country which they govern is. Bitcoin is an option to get around inflation. It is a choice. And I do not believe it will replace any currency.