I kinda see two issues here, first, the only possible reason for registration, if future confiscation.. There is no other possible reason for this to exist. They'll start with single makes and models, such as the Bushmaster AR.. they'll do this by ramping up the angst and fear.. The next phase will be to ban or prohibit, variants of these guns.. which is ever AR in the US. If this flies, they'll then get a committee together, made up of professional victims, expect the Brady Campaign to be represented, in some cases, having power to enforce their agenda, by the committee being numerically stacked. That's what happened in Canada..
The second thing I see, is by specifically going after certain firearms, they are hoping to polarize the firearms community, this worked in Canada, when, they went after things like AR's, the owner of a 30 30 Winchester, couldn't care less about your rifle in lots of cases, as long as they leave his alone. They then started funding assistance, to various provincial hunting/shooting organizations, to 'train' people.. they then made it clear that the funding would stop, if they got to uppity.. as a result, our collective voice was sold, like a $20.00 hooker.
Frankly, I think that you may have to follow Canadian shooters policy of committing the largest case of civil disobedience in Canadian history.. we didn't register, we didn't turn in, we refused to fund organizations that prostitute themselves, and got ready for the next election. Ultimately, we completely destroyed one long term political party, the second one is effectively nonexistent,..
The last possibility is that the various alphabet agencies will try to forcefully confiscate the firearms, if that's the case.. your Bill of Rights, provides the answer.... You have to understand, you've just got yourselves into a battle, there is no compromise, ever, for every inch you give up, they'll demand something else..
Good luck people.. and keep your powder dry..