I think they are also manufacturing Gen 3 for military and law enforcement contracts, where they have to ship models that are compatible or identical. I have no idea how big that business is compared to the California civilian one.
The US firearms market is by far the largest in the world, about half of the whole world. And California is roughly 10% of it, or a little less. For grins: The total number of firearms registered in Austria is about 1.5 million, and Austria is Glock's home country; California has probably about 10 million guns legally owned, and handgun sales alone in California are about 700K per year. Assuming roughly half the weapons in Austria are handguns (that's very optimistic, as most European countries have more hunters than target shooters), that means as may handguns are sold per year in California as there are total (not sold) in Austria. I'm going to bet that more Glocks are sold in California than in any other country in the world, excluding "the whole US". It's possible Texas has California beat (the gun market in Texas is usually roughly the same size as California: lower population, less disposable income, but more guns per capita.
The current barrel bill only requires transfers of barrels to go through an FFL; it does not restrict what barrels and parts can be sold. As you said, that could be added in the future.