The Ex Post Facto would seem to apply, but who knows, as has been stated in this thread, it will take months to years to get through court and by then your RAW will have been a soda can 10 times over. Fact of the matter is, California has done this in the past with the SKS. I am not sure if that was later overruled, but lots of ppl lost their guns in that move.
As to your point about a court case to stop this. A bill has no force of law, it has not passed, so no court is going to take it up. After it passes, and when someone with standing challenges it, is when a court can look at it. Probably start in federal court, appeal to 9th circuit, then to SCOUTS -- years.