Please keep in mind that there is a huge difference between the war on drugs and confiscation of firearms - the drugs aren't legal. A far better analogy would be Prohibition, due to a legal product suddenly being made illegal.
Another difference is the paperwork tracking legal purchases, even if it's nothing more than the 4473 forms. It's a starting point to go after the law abiding that doesn't exist for the illegal growers/smugglers.
I think the last item that will make this a very difficult and unworkable idea on the national level is the depth of history of firearms ownership in this country. Certain states/locations will be far more likely to "hand them in" peacefully due to the leftists drumbeats of how terrible guns are for the last 50 years, like Hawaii, New Jersey, NYC, etc. Others, like Texas, Wyoming, Montana, Arizona, etc., will be FAR more resistant to the idea.
Thank you for the link - I shared it on facebook. It's amazing how many people also think that confiscation can never happen here, and are shocked to the core when shown proof that it has already happened.