Here in the US, beyond depending on owners voluntarily complying with demands to provide input and comply with whatever law, the only recourse would be to have the ATF confiscate all the ATF Forms 4473 which currently is against Federal law for the government to have and hold.
I for one would never comply with an order to ‘register’ any weapon I might own. I’ll secrete, disperse and distribute before I do that.
When the government decides to, they’ll go to the gun shops, confiscate all of the 4473’s, and proceed to go door to door confiscating any and all weapons that they find. Why do you think the feds require that dealers keep those records? Easy local access to conquering forces, that’s why.
As a disclaimer, according to official government records, I have never owned or purchased a firearm of any kind. Just look for any 4473 with my name on it. And they will.