Your point #1 - agree manufacturers won’t want to make a California only version, but suppose they instead just up the price and include this feature in all their products ?
Why would they wish to do that? It could add as much as $100 to the price of every gun, plus it would make replacement parts harder to make and more expensive to sell. This would price guns out of the reach of those who need them the most - the law abiding with little money living in bad neighborhoods.
Plus, considering the world arms market doesn’t require it, most of their customers don’t want it, and S&W showed them what happens when they make a deal with the devil, why on earth would they do that?
And no one will buy them.