Thank you for this really valuable toolchain, which I have been using with increasing success over the last few months. The recent <pre> version of the asciidoctor-epub3 gem is a wonderful addition.
I find the most frequent use case which stops me using Asciidoc/tor, though, is verse. I realize that the limitations are largely a limitation of DocBook, although the DocBook Publishers official variant schema does include some basic additions (speaker, line, linegroup, poetry, dialogue, drama). TEI-Simple has a more extensive set of elements.
I also realize that it would be possible to include pass-through codes to achieve customized output, but this looks a bit daunting at scale, and maintaining this kind of system loses some of the advantages of the powerful 'out-of-the-box' transformations of the Asciidoctor toolchain.
I see that the last discussions on this topic are a few years old. Has there been any further consideration given to extending the built-in verse-related element set?