[Someone]

If I understand this correctly, this leaves the options of either keeping the existing chip that knows your face but isn’t backdoored, or replacing it with one that is backdoored but doesn’t know your face.

If so, I think it would slow down the NSA. They would have to figure out how to add a new face to an existing chip and, ideally, keep that hidden from the phone’s owner.

[sudosysgen]

But you've just owned the screen. If youre the NSA you'd be exfiltrating the screen data and inputting touches (see TEMPEST)