If we just put a scenario that country "X" decided to make owning and using crypto illegal, how are they gonna force this ?
They can't keep on tracking each and every address. We can make millions of one-time use addresses on different wallets with different identifiers and it'd be impossible to link them together (if done the right way).
This means it'd take so much time just to track one person's transactions. Which basically means applying such things on a large scale (making it a law) is practically impossible and would need an uncountable number of human resources.
I think the status right now is that governments don't really know what to do. They surely are aware of the existence of bitcoins. It's no longer the small thing on the side that passes unnoticed. But they still have no idea what to say or do about it as it's something that's totally out of their hands. On one side, they don't want people to evade taxes and don't want their printed currency to be obsolete and at the other side they can't just reject it. I guess they're just waiting to see how things will turn out.
They can't do such thing.