Earlier quoted context omitted.
Every camera will have a unique key so a single key leaked is still no issue. It's easy to maintain a blacklist - similarly how CRLs work.
So now we are essentially bricking the devices of real users? Without doing anything meaningful to real attackers who just grab the next key out of their list of 10 million stolen from insecure androids.
It shouldn't be easy to extract it and that's it. It's even less difficult than keeping the DVD/Blueray keys secure because each device has a separate key, so if a line of devices gets compromised easily it's easy to spot.
Then you put a legal framework around what can be presented by media, the requirement for signature collection and so. And one of problems with photo/video authenticity is essentially solved.