THEY WOULD DO IT TODAY IF THEY THOUGHT THEY COULD GET AWAY WITH IT. DOZENS OF RAT POLITICIANS HAVE SAID AS MUCH.There's a REASON the DHS purchased over a billion rounds of ammo, and more than 2,000 anti tank trucks. Now, why do you suppose that is, hmmmm? (Yes, that's a rhetorical question.
As for what it would take for confiscation, California now has an ongoing confiscation program for people who own registered guns (how convenient) but become ineligible due to a conviction or mental issue. From what I read, they send nine cops at night to surround the house, then knock. I don't know if anyone has ever tried to fight them yet, but a single sleepy person would definitely lose that fight.
If there were social unrest and people getting organized, it would probably explain why an armored vehicle might be handy.