For use in their main computing device, people would like an e-ink display that could reliably pull 30+ FPS while not costing a fortune, and preferably with some color capacity. They don't want a display from Kindle. Until the gap between that and what we have today is closed, the demand signal won't register.

FWIW, there was a huge initial demand back in the Kindle era; the e-reader use case was absolutely perfect for these screens. Nowadays, from what I can tell, the main demand for e-ink is in retail, for cheap electronic price displays. But that doesn't drive the progress of e-ink much, if in any way at all.