It will need a non-corrupted-government to be a reality. I'm afraid this is going to be very difficult to achieve in so many countries, despite it is a great idea, for the current situation in too many places is corruption as a daily reality.
Anyway, taxes are already being applied in some countries, as long as the crypto convert into fiat and depending on the amount you get in the transaction. For instance, in Spain, you will need to pay taxes if your crypto selling activity is more than 1000 euros, as far as I know. But, of course, the taxes are not invested in any activity related to crypto security.