Overall, the new styles are an improvement on the existing styles. However, because the restyling happened after the 2019 conference and long after the papers were written (and because authors weren’t provided with a sample of how to properly tag footnotes and references, etc.), the 2019 proceedings are in a limbo state where most of the remaining improvements require changes to the source that no-one has the time, energy, and authority to change. The authoring framework can help future authors, but it was developed too late to help the other 2021 authors.
The process of developing the new styles resulted in multiple improvements to the DocBook XSLT 1.0 Stylesheets and to the XSLTHL syntax highlighting utility.
Developing the customisation has been sporadic, and it is still a work in progress. The code is available on GitHub [MUK-xsl] for anyone to copy and modify. Comments and pull requests are welcome.