[pfg_]

This seems like a non-problem, cut the display resolution in half on one axis and reserve two 'subpixels' for each pixel. Then you have a full color display with only one physical pixel type and that needs one less subpixel. These displays could even produce some saturated colors with specific wavelengths that can't be represented on regular rgb displays.

[ajuc]

You'd still be unable to produce different brightness pixels. You'd get white but no grayscale.

I guess you could cheat it by moving the wavelength outside the visible spectrum?

[mark-r]

I hate to think of the damage large amounts of IR or especially UV would do to the eye.

[enragedcacti]

Assuming they can PWM the brightness while getting consistent color (seems reasonable since microLEDs have extremely fast response time) then I think what you're saying would work great. It would be akin to 4:2:2 chroma subsampling where luminance (which we have higher acuity for) gets more fidelity and the resulting image quality is closer to full-res than half-res.