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Indeed some as yet unknown tech is needed unless Qualcomm sell off all the IP etc in Mirasol to Samsung, Sony or someone Chinese.
Actual eink coloured by filters in front of the pixels can never be bright enough without front lights, because "white" would be additive sub-pixels of red, green and blue. CYMK on paper is bright because it's subtractive. The white is no ink. Yellow is only the blue removed, Magenta is only green removed and Cyan is only red removed. The RGB filters on a display remove ALL light except red, green or blue on every dot.
This is why it's not about technology or better manufacturing for ambient light reflective displays. At the least you need clear pixels that reflect all the light for white. Even Mirasol would be poor for monochrome compared to eink and really poor compared to CYMK paper printing and it's the best alternative to LED or OLED.
The reason that reflective LCD is very rare and only used on monochrome is that LCD needs two polarising filters. If perfect you'd lose half the light. In practice they are slightly lossy and reflected light has to pass twice. The 1/4 or worse transmission of the R G B or RG and GB (alternate lines) sub pixel per colour pixel loses the light twice on reflection. Most of the power consumption is the backlight. Even for "white" less than 1/5th is visible. OLED isn't actually usually real LEDs, but blueish Electroluminescent spots with phosphor. Real R G B LED displays do exist and are more efficient, better colour and longer life than OLED.
So an ambient light colour ereader needs CYMK technology where a white dot is a clear cell rather than R G and B visually averaged. That concept of technology only exists for photographic film and ink on paper.
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