The only real issue I see here is the requirement to jump through different hoops to ensure you are "legal". With all of that, when SHTF will they have access to the records to prove that the firearms are, in fact, legal? Let's look at Katrina. Access to records of that sort woldn't have been available to anyone - local, state, or federal.

Are we to assume that the government will err on the side of the person in psssession of the firearm, or will they confiscate the weapon with a promise to return it if everything is found to be in order at a later time?

As others have stated, the 2nd Amendment is supposed to be enough to protect us from that very thing.