It’s a barely hashed together spec for associating webpages. It doesn’t seem to offer any of the “value” that social networks do, the prime of which being an easy-to-initialize profile with copious features.

It could be possible with nerds/geeks. However, that group (in the early 00s, at least) was far more interested in keeping their online anonymity prime and avoiding social networks; so I could totally see why it was dead in the water.

Around 2007 or so I worked on a semantic web search engine.

Among other things it ingested xfn (and foaf) so you could reasonably look for things like the connection between you and someone else who had a webpage, but the whole thing by itself didn't replace in any way what social networks were already offering, e.g. your feed, or direct messaging.

I think WordPress still supports xfn links, but it's not particularly useful.

> Is this still a thing

Today's webpages are mostly a big pile of javascript generated Single-Page-Application™

So no it's not a thing. The HTML is barely parsable.