> I'm hoping to replace it with Typst

This might be stupid but is there a reason you want to go through docbook and xsltproc instead of setting --pdf-engine=typst?

Looks like it's getting there, but still needs some work. It's not obeying the book output or number sections. I can probably get the indexing going, though.

Measured at 10x faster than LaTeX.

Yes. Two reasons:

1) More control over the typst output... 2) I didn't know you could do that. :D :D :D

I'll check it out--thanks for the pointer!