This seems to be specifically designed for people who are worried that their communications device has been pwned over the internet. So, people who are under fairly targeted, active surveillance.

Hence requiring three physically separate computers and data diodes at each end, to try and physically prevent attacks over the network.

The way I remember it being explained, is in the US metadata had particularly poor legal protections compared to the message content. This is what gave the government any sort of legal basis to claim mass surveillance was legal, compared to say recording and indexing every message from every american. The context of the talk was about cloud and data sovereignty, and making the case that it isn't unsafe to store data in the US with the revelations at the time.

I don't think the talk was recorded, I wish it was, because I think that was the best description I've seen from a legal perspective on why the surveillance programs were targeting metadata and not contents.