Glooming bottom line:

So what's the way forward for blind screen reader users? Sadly, I don't know.

Modern text to speech research has little overlap with our requirements. Using Eloquence [32-bit voice last compiled in 2003], the system that many blind people find best, is becoming increasingly untenable. ESpeak uses an odd architecture originally designed for computers in 1995, and has few maintainers. Blastbay Studios [...] is a closed-source product with a single maintainer, that also suffers from a lack of pronunciation accuracy.

In an ideal world, someone would re-implement Eloquence as a set of open source libraries. However, doing so would require expertise in linguistics, digital signal processing, and audiology, as well as excellent programming abilities. My suspicion is that modernizing the text to speech stack that is preferred by blind power-users is an effort that would require several million dollars of funding at minimum.

Instead, we'll probably wind up having to settle for text to speech voices that are "good enough", while being nowhere near as fast and efficient [800 to 900 words per minute] as what we have currently.