There is a lot of ways of imposing a tax for the government's rising fund which is used for the expenditure for maintaining a state properly, I think only BTC is not their headache, Another thing is that, If Bitcoin would be included in the tax system then what is the problem, I don't see any problem at all, We are giving Foreign exchange when we convert BTC into USD and Covert into local fiat, so we have already given to them, so there should be a proper system which only once imposes tax for using BTC or Cryptocurrency, I think it's not a difficult thing anymore.
Every government tax based on the holdings we've got. This can be property, assets, shares, stocks and other valuables (Gold, bonds, policies). Here Governments find it easy to have every information added to their database as everything is centralized and subject to provide information to the government. With bitcoin and other cryptocurrencies information on holdings of people can't be found exactly until the person himself discloses. This way taxing of bitcoin isn't easy.