The display and the business end of the equipment are critical and should not be network-connected (or even have USB ports, for that matter). The part that uploads to whatever big server should have updates all the time. The critical bit should either be connected to the non-critical bit by a genuinely one-way link (e.g. unidirectional fiber) or should use a very small, very carefully audited stack for communication.

This is all doable, but it adds a bit of BOM cost and changes the development model.

An alternative would be to expose these subsystems on a network and have strict API's, encryption, and authentication between them. This would allow you to audit/update components individually rather than the whole device. So your display would act as a networked display and only have a very limited set of functions.

Yep. That worked fine for the Iranian uranium centrifuge guys...

stuxnet jumped airgap over usb, did it not?

We already have that distinction in our current regulations... some devices need FDA approval, some don't