PDFs produced using latex are not accessible.
We could introduce a command-line option that causes the latex writer to include annotations for math (perhaps using the unicode fallback or even raw tex), image alt text, and more:
http://ctan.math.washington.edu/tex-archive/macros/latex/contrib/oberdiek/accsupp.pdf

This package also includes an option that makes spaces visible to copy and paste (often when you copy from a latex-compiled PDF, spaces disappear).

Structural elements (paragraphs, lists, etc.) need to be tagged, and reading order indicated.

See also:
https://www.tug.org/twg/accessibility/
http://web.science.mq.edu.au/~ross/TaggedPDF/
https://tex.stackexchange.com/questions/124291/revisiting-producing-structured-pdfs-from-latex (with information about using ConTeXT)