The LaTeX expression $A$ is getting translated into

<emphasis role="math">A</emphasis>

which should generate italics, shouldn't it?

And a related question: is it possible to generate non-italic text inside ? I am looking for the equivalent of \mathrm in LaTeX.

From Sanders:

By default, our toolchain does not render with a custom role in italics. I've customized this handling so that anything tagged as will now render in italics.

If you want portions of text inside an block to be non-italic, you can use an tag for that, like this:

This text is italic, except for this bit

I think this is all you need, but let me know if you see any issues or need anything further.

I added a renderer for mathrm in Renderers/DocBook/book.zpts

name: mathrm

And that works.