While there is no limit to the depravity that our government will descend to, I doubt that gold confiscation would work very well in this day and age. The population in the 1930s was looking to the government to solve their problems (sound familiar?) and they rather meekly went along with the demand to hand over gold for paper at $20 an ounce. Only a short time later the evil FDR changed the exchange rate to $35 an ounce, devaluing the currency. People remember that, and trust the government less.
The method of confiscation is unlikely to work very well again. FDR posted armed guards at all banks, who went with every person who opened their safe deposit box, and made sure any gold was traded for worthless paper. Lots of people owned gold then, and many kept their coins in bank safe deposit boxes. Today, very few own coins, and those few tend not to trust banks very much.
Quite a bit of gold was never turned in; literally billions of dollars went into hiding and/or overseas. You can still buy 1920s St. Guaudens coins at most coin dealers.
So don't keep most or all of your gold in a safe deposit box, and if you do, keep your eyes and ears open. As pointed out earlier, these criminals don't move very fast, and they telegraph their intentions if you just pay attention.
If the government tells the citizens to turn in their gold coins, cries of "Molon Labe" will ring across the land, and those "tiny gilded cylindrical lead ingots, and short brass tubes" will ring out their own song as well.
Now's a great time to buy gold and silver; they are in the midst of a major correction, or manipulation, depending on what you know and believe, but the price is as low as one is likely to see for some time.
Peace,
Silver