My point is that Apple currently does not appear to have tight control over the serial numbering or whatever on the external components (display, etc) in a trul

My point is that Apple currently does not appear to have tight control over the serial numbering or whatever on the external components (display, etc) in a truly secure way. If you let anyone re-pair devices, then that opens the floodgates to 3rd party vendors being able to make devices that appear as 'authentic' components, which does not accomplish #2. As it stands today, you can already use any random components, you'll just get a pop-up telling you it can't be authenticated.