California is too big of a market. Everyone will just conform to the California standard.
The California standard is completely and utterly infeasible. It fails Goodhart's law, which states that as soon as a measure becomes a target, it ceases to be a good measure.
As soon as you say "A part that looks like this arbitrary gun part cannot be manufactured", it's open season on designing a new version of the part that doesn't trip the rule. And as soon as the government adapts to that new design, five minutes later, there's another new design that still doesn't trip the rule.
It's a game of cat and mouse, but there are infinite numbers of ways to design the part, and only finite storage for models to recognize the part.
Basically, the game is already lost before the government even starts to play. The only way this would ever work would be if you were required to provide documentation telling why you're making each part, and what it is, and having someone validate that the part is plausibly what you say it is based on it looking like something you are allowed to print, and therefore presumably not part of a potential gun. And even that wouldn't be foolproof.
But as soon as the presumption is that it is okay to print something unless it matches any sort of pattern, model, etc., you're screwed. This can't be done, period, or at least not in any way that will meaningfully prevent... well... anything, really.
And besides sooner or later somebody is going to use one of those ghost guns in a murder and it's going to get around and make the press and the public is going to demand action.
No, they won't. Nobody will care. Just like they don't care about all the murders that happen now. The only way somebody cares is if some blowhard politician screams, "Oh, my g*d! It's a ghost gun! Everyone has to panic and be outraged!" And then they will care. But as long as the people in power don't act like morons, someone will use a ghost gun, and there will be exactly as much of a response as for a murder involving any other firearm, because it really doesn't make a dime's worth of difference in the end.
People freak out if you threaten to take their guns away. But they also freak out if the cops can't catch murderers easily. And easily producible untraceable guns that don't require a machine shop or something the public isn't going to allow.
Traceable guns don't catch murderers all that often. The overwhelming majority of gun crimes are committed with guns that were not purchased through a legitimate dealer — almost 86%. Even if the serial numbers have not been removed completely, you'd end up tracing the firearm back to the person from whom it was stolen, rather than the actual killer.
There is basically no benefit to serial numbers on firearms from a public safety perspective, and there never was. The only real benefit is getting stolen firearms back to their rightful owners. And while that's a laudable goal, the people pushing it as a way of preventing crime are being completely disingenuous.
The people pushing fear of ghost guns are doubly so. Every gun used in a crime is a ghost gun. The only difference is that someone of them were manufactured, and the rest were just de-serialized.
Anyway, my current plan is to figure out whether my assembly member voted for this trash, and if so, pledge the maximum dollar amount to the campaigns of every person running against that person in the next election. If everyone reading this post did the same, these shit-for-brains-stupid laws wouldn't keep getting passed.