@SteelWagstaff, I was looking back to see if Prince had responded on your initial inquiry and saw you had recently followed up for an update.
We will need to investigate! One issue is that MathML is often pre-processed by JavaScript libraries like KaTeX and MathJax, which might complicate the accessibility story.
Hopefully their investigation results in PDF 2.0 adoption but just wanted to thank you for keeping on them for this support request!