If anything medical devices, especially implants, should be modifiable. Otherwise you're stuck with an unmaintainable device (possibly in your body) once the manufacturer goes out of business or the support window ends or whatever. Right to repair and all that.

And this is a very real concern. https://spectrum.ieee.org/bionic-eye-obsolete

For external devices breaking some big, visible "last inspected on XX/XX" seal to do so would be acceptable.

For payment terminals you could do the secure boot thing where replacing the manufacturer keys and flashing custom firmware wipes the TPM storage.