Russia already have this, they created a cryptocurrency backed by their own currency, and some other countries. And people that will earn using it should pay taxes while the supply can only be distributed by the government. So what I mean is if governments will create their own cryptocurrency, they will surely make it a centralized one, in that case they can still control the flow of the money, opposite from the original concept of cryptocurrency which is being decentralized. And of course they will benefit from it because they will put huge taxes to people that will earn from it.