It won't happen. That would spell disaster at the polls worse than a "Grandfathered" ban would, for any Senator or Congressman who voted for it. Many people have extensive collections of these weapons. Raping $200.00 out of the pockets of citizens for every one of them they own, would all but cause riots. Not to mention bog down the ATF with a mountain of paperwork. You're going to be hearing a lot of this type of idiotic talk coming from liberals in the next several months.
Luckily, it seems the more they talk, the harder they make it for themselves. They will just exemplify their stupidity on the subject, and in the process show how detached they are from it, let alone any real "solutions". Next will come a "parade of victims and their loved ones". They learned that trick from Sandra Fluke. Find a living, breathing, mass of protoplasm to support your cause. Then stick it out there for all the world to see and snivel over.