Quarto is a far bigger platform than R markdown. But, this is limited to only rendering markdown or its flavours with R or the like code sequences only.
Asciidoc is simpler has only one flavour with distinct features for writings very good books, articles and what not?
Therefore, I request its developer's to incorporate rendering facilities for Asciidoc documents to be written in Asciidoc quarto.
What you are pointing out is that, when one writes a document in Quarto Markdown (Pandoc Markdown), then it can be converted to Asciidoc codes file, which should be rendered elsewhere. What I mean is that the output quarto rendering is a file with asciidoc codes, not the html, pdf nor docx.
What I am expecting from Quarto is that we should be able to write the documents, along with R scripts in RStudio in .asciidoc (or .adoc) code format, instead of Rmarkdown or Markdown, and it could be rendered to html, pdf, docx or docbook.