I suspect Apple has ways from the factory to fix this. Secure Fuses that can disable code paths, or inject code. But unpatchable in the field.

Future devices can be fixed at the factory. That still leaves tens of millions of vulnerable devices which are, as repeated before, unpatchable.

In the factory, Apple can just create new hardware without this flaw.

That would be in the fab, not the factory, might mean tossing out inventory, and will take longer. I'm guessing they will do both.