I don't think confiscation is even a possibility at this time. Since probably less than 1% of the general population owns gold or silver bullion, and since for years governments have been selling bullion by the ton. But, if buying gold and silver becomes popular to the citizens due to the dollar dropping and gold and silver rising, and it becomes the "in thing" to own gold and silver bullion, then perhaps confiscation would be considered.
For confiscation to happen, I believe the dollar would have to be near total collapse and gold and silver would have to be worth alot more than it is now. If the dollar totally collapses I could see the gov want to create a new currency backed by gold or silver, to gain credibility in the world markets, instead of paper fiat backed by nothing.
But like any other investments, when Joe Six Pack and the average people around the water cooler at work who currently don't even know money was once gold and silver start getting in, it is time for me to sell and get into something else. When any investment becomes too popular and it seems like an eternal fountain of profits, it is time to take profits and run. Gold and silver will be that next great investment that the masses will run to.
Just like the recent tech stock bubble and real estate bubble, there too will be one for precious metals I believe. Just not yet.
Jim