This question is more than speculative, and it is one that is bound to come up when talking about storing wealth in precious metals, and especially where gold is concerned. History is replete with governments concocting new schemes to steal wealth from the people they are supposed to be serving and protecting--and the US Government is no exception.
"On April 5, 1933, under the pretext of a national emergency, President Franklin D. Roosevelt issued Executive Order 6102, making it illegal for U.S. citizens to own gold.
The decree forced Americans to sell their gold at an artificially low “official price.” If they refused, the government could hit them with stiff penalties: a $10,000 fine (equivalent to $205,000 today) and/or up to 10 years in prison.
The government blatantly stole wealth from the American people.
Many worry the U.S. government might confiscate gold again if it becomes desperate enough. I don’t think those fears are unfounded. The U.S. government’s abysmal financial situation is only getting worse.
But would it really do a 1933-style grab again? I don’t think it will. However, there is another growing threat to your gold."
The rest of the article over at zerohedge.com offers some ideas on ways to protect your gold assets from a future grab. (You can read it over here.) But even still, it's always been sound practice to diversify!