Since nobody answered to this, I will try to answer. This is a point that has not been touched in example questions so this is more my opinion than something deducted from what has been voted on.
This proposal is mainly intended for ebook reader devices and the formats in which ebooks come (epub and mobi). I would not count pdf to these formats, but the problems a visually impaired person has are probably related to those one has when trying to view a large pdf on a small reader. In both cases one effectively tries to enlarge the content without losing its structure or extract its text to reflow it (or have it spoken).
Functions for the visually impaired in ebook readers (text-to-speech, menus read aloud) would definitely be on topic.
Ebook reader software compatibility with screenreader software would probably be on topic, because those are things closely connected to the formats (and possibly drm).
Reading pdfs is something I would see as off topic. SuperUser is probably a better place for asking questions about this. But I am not sure about this.
Screenreaders alone (without connection to another program) on any other device than a dedicated ebook reader is definitely off topic.