Right now, DT can speak anything I highlight, but it can’t yet speak the whole document to me – which I’d love. I’m hoping that’s a small tweak, since Scrivener & other apps have this power.
Please define "“a whole document”, e.g., a 500 page PDF or a single rich text file?
For me, it’d be the 500 pg. PDF file.
I do a lot of research and have many books stored in DT, so I’d love to be able to listen to them on a walk, driving, or at home — in addition to reading them. I also write fiction/etc. and would like to have sections read back to me. Plant the cursor somewhere and have them start speaking from there.
Thanks for considering.
Sadly, there is no simple mechanism for this. You could potentially script speakign a smaller document but there is no function to read such large volumes of text. You would also have no ability to start and stop at any given point, so unless you wanted to hear it from the beginning each time, scripting is not going to help out 
I don’t mind hearing it from the beginning each time. I can plant the cursor where I want it, or left off. Scrivener has this feature, and it’s not elaborate — just start speaking, and stop speaking. The cursor doesn’t move with it, so if you stop and don’t relocate the cursor, it will start in the same place. Does this mean it’s possible to create a script for this?
Not with that volume of data or dealing with insertion points in the text, no.