Your out of hand dismissal of this is to point at technologies that practically no one uses in total and definitely no one uses for the scenarios the author is referring to (e.g. search results)?

You think suddenly everyone is going to start signing their tweets and blog posts and people will en-masse assign a trust score to said content based on the people they know and trust in their PGP keychains?

I'd like that world quite a bit but it's decidedly not going to happen - probably at all and definitely not at scale. Are you so sure that's what we'll all do in response to automated content that you're calling this article a "sky-is-falling thesis"? If so then I'm genuinely baffled by your confidence here. Where does it come from?