If that day would come, then definitely there will be tax to be payed from our cryptocurrencies, because it is clear that the government wouldnt allow cryptocurrencies to rule the world without them getting something in return, so its for sure that cryptocurrencies will be taxed, but that is only what I think, there are still other bigger matters to be discussed that the government has to put their minds on, as well as the whole crypto community. But, let say that bitcoin becomes our universal coin, or money, then that would be great, having to go anywhere without bringing any cash with you, that is just safe and convenient.