I wonder if you can add a TTS engine to Android as an app or plugin, then make Moon+ Reader or another reader to use that custom engine. That's probably how I'd do it for the easiest approach, but if that doesn't work, I might just have to make my own app.
I’m planning on making a self-host solution where you can upload files and the host sends back the audio to play, as a first pass on this tech. I’ll open source the repo after fiddling and prototyping. I’ve needed this kinda thing for a long time!
Please make sure to link it back to HN so that we can check it out!