There are more HDCD recordings available than SACD and DVD-A combined. It was widely used, but lost momentum when Pacific Micro was bought by Microsoft. Many, if not most, HDCD encoded recordings are not even marked as such.
Why HDCD did not become a dominant format?
I've been listening to Reference Recordings 30th Anniversary Sampler while evaluating a Sony NS 9100ES and it was so obvious the HDCD decoding through my modest older Toshiba SD 9200 was "vastly" superior to the new Sony playback. I just don't understand why HDCD did not become the new standard as the musical quality is much enhanced. What happened?