Besides, the fab itself isn't the issue. Rather, the equipment used during the fabrication process itself are the weakest link, so to speak. Further, if we consider the feasibility of insider attacks, the people who maintain the fab are potential targets as well.
So, I think achieving what you propose would require: 1) access to an immense amount of resources, 2) the capability to self-manufacture the tools required to manufacture ICs, and 3) an AI that can operate the fab.
The third point alone is so far off that I'd conclude it's going to be impossible for a long time.