ARIA and accessibility microformats were separate from the ones the fediverse was excited about (and thus the GP was talking about)—things like hCard for identifying people, places, and things. Accessibility is useful to many people, but hCard et al. were probably never really useful to anybody other than Google. Still, many of us back then were obsessive-compulsive about using them in the hope that one day computers would better be able to understand authoritative information about identities and relationships between identities. I still have microdata on my personal web page.