SourceIt is possible, unless crypto holders are exceptionally vigilant. I think we are well-positioned on Hive to avoid a lot of this, but there are some things to keep in mind.
In any asset, all any government has to do is stockpile enough, license it to select business partners, and then restrict citizens' ability to get direct access. In crypto this is harder to do, since crypto is electronic, but in a coin like Bitcoin that will only ever mint a certain amount, a global governmental scramble for Bitcoin could in theory push the price so high that it would be out of reach for most.
However, the price for Bitcoin would need to be at least $100 million so that every subunit of Bitcoin, called a Satoshi, would be $1. That is not impossible, but unlikely in the immediate future, so Bitcoin at least in terms of Satoshis will be affordable for a good while to come!
More likely, governments would change the classification of crypto, making it accessible only to what are called “accredited investors” who need to have a certain amount of wealth already to be allowed to participate, and only through approved financial institutions. As a transition measure, governments can limit how much of anyone's holdings can be crypto – this is being done in the United Kingdom at last report – or make taxes on crypto so high that trading and selling becomes difficult in terms of profiting. The United States taxes every trade, not just sale, so citizens have to come up with USD every time they trade one coin for another for a profit – and there is no word that even the crypto-friendly Trump administration intends to change that.
However, in order to keep a government to get control of assets that it does not own and control initially, but needs to buy, all that is necessary is for those who have said asset around the world to not sell. There are reasons many serious Bitcoiners say that they will never sell. Now you know one of them!