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Why do they do this? To remain in financial control and to stop financial crime like whitewashing of funds from happening. Is it likely to happen? Yes, the US banned holding gold privately in the 1930's. So that the US government was to be a monopoly gold holder in the US.
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So you believe that the US government is the government of the world? It was the US government that did that. Not the world. And I guess you are talking about the executive order signed by Roosevelt, right? Yeah that was shit. Citizens were forced to give up their golds. The order was active for like maybe 40 years.
But I doubt that is going to be a case with bitcoin. Crypto currencies are decentralized. Hence they have no central authority to ban. I mean, no one can stop something that is P2P and decentralized. Look at torrents. Were they able to stop those? Nope.