Sure they did. “ ... the record demonstrates that the limitation interferes only minimally with the core right of self-defense, as there is no evidence that anyone ever has been unable to defend his or her home and family due to the lack of a large-capacity magazine"
If the above is the proper reasoning, then barring you from having a second magazine would interfere only minimally with the core right. It won't take the California legislature long to figure this one out.
The reasoning above could also make the decision easier for the Supreme Court as follows: Because the law in question interferes with the core right of self defense, as admitted by the majority of the Ninth Circuit, the ban is overturned.
The Supreme Court needs merely to recognize that interfering, even minimally, is infringing. The Ninth Circuit has made deciding this case very easy.
They would also have to limit the number of guns one person could own. Of course California’s number would be zero.