I think other companies are already into this kind of thing. For example, there are lots of content verification services that work out-of-band from end-to-end

I think other companies are already into this kind of thing. For example, there are lots of content verification services that work out-of-band from end-to-end encrypted messaging systems. It would be trivial to direct this towards all kinds of "what are people viewing" investigations for new laws and new vpns.