This is a great experience. I wonder how an e-ink friendly version would look like. I don't think word by word would work but maybe sentence by sentence? but then would that break the effect? Either way, I'll definitely try with a book I've been procrastinating on reading ahahah.
E-ink is the frustrating part because it's where people actually read books, yet it's the display least capable of doing this. Partial refresh allows for a handful of updates each second, but it comes with ghosting. At 300 words per minute, which is a word every 200 milliseconds, you'd be reading through the residue of the last two or three words. Full refresh clears that, but it flashes the entire panel and takes long enough that you would only read about a word per second.
Your idea about sentences does affect the experience, but I don’t believe that makes it worse; it’s just a different approach. Once a whole sentence appears on screen, your eyes move across it again, so the no eye movement part is lost. What remains is the return sweep, the long jump back to the start of the next line, and the moment when you lose your place on a dense page. Those are real challenges in normal reading, and chunking by sentence removes both. You would end up closer to guided pacing than RSVP, which might suit a book better anyway.
Let me know how the procrastinated book turns out.