> I don't know much about the accessibility business, but my impression is that the screenreaders are all very expensive. Maybe providing a universal interface as described would level the playing field, maybe that's not desired (by the big brands).

False. I have a print-related disability and I rely on screenreaders.

I use Orca on Ubuntu. However, the default voices for Orca are deplorable (by default eSpeak text to speech engine).

Most people do not know this, but https://oralux.org sells machine learning high quality voices (NeoSpeech engine) for $35 per voice at most which work directly with Orca. Here are the English text to speech voices: https://www.oralux.org/voice.php#english_american_english