What's the current state of the art in Docbook -> Asciidoctor conversion?

I see a few old posts here re https://github.com/asciidoctor/docbookrx, but trying this on some of our Docbook stuff, e.g. one of the .xml files in https://github.com/KhronosGroup/OpenGL-Refpages/tree/master/gl4, just dies with

> No visitor defined for <refentry>! Skipping.

Is there any hope for applying docbookrx to refentry type documents? Or are there other automated converters that could handle this type of Docbook?

Thanks,

Jon