This could happen on a national scale.
I lived in NYC when it was legal to own and register an HK91 and the Mini-14 with factory folding stock. About a year after buying them I got a letter from the Firearms board saying that they were now illegal to own and I must either turn them in to my local precint or show proof they were transported out of state (the latter would not be an option if this was on a national scale).
I do know of someone who never responded to this notice and he was visited with a search warrant and his guns were confiscated. It cost him a lot in legal fees but he did not get any jail time as his lawyer stated his case in that he never received the letter as it was not sent certified.
I moved out of NY as soon as I could. Now with Obuma likely to be the next coke using president this really can happen.