The ATF and DOJ made a determination in 2010 that they were not illegal under the current law. They did not negate law or make law. They can't do their job and prosecute a law that does not exist.
Meaning if someone wanted to make a law, they could. But they could not prosecute under existing laws. Since they were not a firearm, they were a part. Much as the parts are made and sold to convert a AR-15 to a fully automatic weapon without some crazy contraption, just replace a part. Who will go after those parts ? Probably will not be covered under any legislation we get.
MAKING LAWS IS CONGRESSIONAL WORK ! as per the constitution - read it !