This is some multilayered stupidity here.

"We have to do something about these undetectable and unlisenced firearms that can be made in every home without a trace!"
"We should make it illegal to have a concealable firearm!"
"We already did that idiot! What else can we do?"
"We could make a law that makes it illegal to own an unlisenced firearm?"
"No, we did that too!"
"We could ban shooting people?"
"What are you, a vegetarian?"
"We should make it mandatory for all unlisenced metal guns to have enough metal in them so our police officers can detect and arrest them for illegal ownership!"
"Brilliant"

In all honesty though, I'm guessing this will end up with a lot of helicopter parents and soccermoms going to try and push for the banning of toy guns, because you can make a firearm look like one.

Also a lot of cops are probably going to be like "Well, that could have been a 3d-printed concealed weapon!" when they shoot a kid and after that outrage, they'll pass the law instead of ever getting proper training for their law enforcement officers.