All this section describes is how to use an HTML link element to associate a lexicon, but do we need to explain that, and is the EPUB specification even the right place for it?

Lexicon files also never needed to be a core media type as they've never required a fallback (the exception on linked resources is also broader, so we don't have to say anything about the "pronunciation" rel value).

We don't have a section on how to use CSS 3 Speech, for example, so do we need to persist this section any longer? Nothing is invalidated from an authoring perspective by removing it that I can find.

If anything, the section should be a separate note as it defines behaviour that should be supported by browsers. (We really shouldn't have defined the speech features in isolation in IDPF.)

I'm fine leaving the reading system recommendation to support lexicons and the speech module for aural rendering, even if support hasn't materialized.