DNS-based CDNs are also effectively this: collect metrics from a datastore regarding system usage metrics, packet loss, latency etc and compute a table of viewer networks and preferred PoPs.
Unfortunately hard documentation is difficult to provide but that’s how a CDN worked at a place I used to work for, there’s also another CDN[1] which talks about the same thing in fancier terms.
Akamai talked about it in the early 2000s. Facebook content folks had a decent paper describing the latency collection and realtime routing around 2011ish, something like “pinpoint” I want to say. Though as you say was industry practice before then.