I don't think if a currency legalized in a country it won't have a tax deduction I am sure it is have a tax deduction when you pay or buy something using bitcoin. And I think it would be easy to the government to put the tax deduction in any transaction of bitcoin if that's gonna happened in the near future.
When bitcoin become universal and the whole world start using only bitcoin and there is no other currency in the market, people will feel ease and happiness because they will be able to use their coins all over the world without any bank transactions and exchanging. They will easily use their wallets for payments. People will enjoy cashless society.
Maybe that won't happen or that's really far from reality, fiat won't be removed from each countries since it is the basis of their nation, bitcoin can be adopted as an alternative currency and can be used all over the globe, that can bring quick and easy transactions to us who support bitcoin, as we don't need to bring cash or card while enjoying our journey even outside our own country.