Re: It's simple
In fact, key escrow systems have been designed that would serve this purpose fairly well.
But that is NOT what they are talking about:
“There's been ideas around for decades that you should create some kind of key that law enforcement can get access to … that's not what we're proposing... "
Despite assertions to the contrary, it would be possible to make them reasonably secure against theft - at least as secure as could be done for any other data.
I stopped reading your comment at that point :)