Always listen to the enemy. They will tell you what they plan on doing to you. Believe them.
For confiscation to occur, one has to identify who owns which firearms. That raw data has existed since 1968 with the passage of the 1968 Gun Control Act and ATF Form 4473.
Since the administration of POTUS #44 BHO, we are living in a post-Constitution nation.
Once the DemonRats regain control of both Houses of Congress and the POTUS they will revive the 1994 Federal Assault Weapons Ban with a few revisions making it illegal to own an assault weapon (by whatever definition they choose). The original ban was supported by the courts despite many petitions of repeal on grounds of violation of the 2nd Amendment.
It won't be hard to digitize all the Form 4473s and load them into a database (currently illegal), i.e., a national gun registry. It won't be necessary for all of the "assault weapons" in private hands to show up in the database for the eventual confiscation to effectively disarm the U.S. citizenry.
DemonRat 2020 presidential candidate Elizabeth Warren said 2 days ago that she would support "super duper IRS enforcement" of the tax code to fund her communist goals. Anyone who filled out an ATF Form 4473 will have the IRS's "mark of the beast". The DemonRats will put the burden of proof of ownership or transfer of the weapon on the private citizen.
Once the new AWB bill is passed and the national gun registry is in place, DoJ will designate firearm collection centers across the land. The IRS will then issue notices to all citizens in the national gun registry who own assault weapons to surrender those weapons by a drop dead date. The notice would say that if the citizens don't comply, the IRS will freeze/seize their bank accounts and levy a fine until the firearms are surrendered. Few people will be able to withstand that kind of pressure.
There won't be a need to risk LEOs going door-2-door to confiscate firearms. The DemonRats will direct LEOs to stage some raids on high-profile citizens who resist. This will be for propaganda purposes and intimidation of the sheeple.