I don't find that "memo" particularly damning - it analyzes an issue and says "in order for X to work Y would have to happen" which is what a good analysis should do. It doesn't mean that Y will - or can happen. But let's assume, arguendo, that they try to implement this memo and "ban & confiscate all guns". How will they do this? They would need either a Constitutional Amendment or a decision from SCOTUS that contradicts a long line of cases culminating in Heller. Both of those options are out of the realm of possibility.
In other words, this ain't happening.
When it comes to getting their way, ...to the powers that be, nothing is outside of the realm of possibility.
Seriously, there are things we do today that years ago would have been considered out of the realm of possibility.
Where was the required Constitutional Amendments that brought in the Patriot Act & the NDAA.
From where I'm sitting, they amended the 1st, 2nd, and 4th amendments right out of there the moment they were signed into law.
The price of freedom is eternal vigilance, ...and heaven knows there have been a lot of shenanigans and hijinks slipped in while people's attentions have been diverted elsewhere.