EInk has a refresh time. Which is a significant mismatch to the flight speed of devices which seek to mask themselves against changing background. More to the point, optical detection is the least worry in this space. by the time it's visible in motion, its already a problem. '
For on-the-ground, its easier to put it under a canopy.
EInk does nothing for radar, or thermal imaging. So your proposed conspiracy is to defeat human eyes, which rarely if ever are the first-spotters. The circumstances where using radar breaches your own privacy are understood. I would expect an ML vision system could defeat this anyway. (and I say that as a bit of a long-term non-believer in AI)
I love a good conspiracy, but alas, I think this isn't it. The grassy knoll is just, after all, a patch of grass, and not an EInk facsimile, in my personal opinion.
(Admittedly, I was being a bit silly with the missile use-case.)
I occasionally see referrals in flow text to a Chinese claim they invented "holographic quantum" radar and can see all current stealth low echo aircraft and subs. I suspect it's bullshit but in war, if stealth was a purturbation, and deep water subs a more historical perturbation toward MAD and now, this is another perturbation much as drones have altered the symmetry for tank and mechanised ground warfare.. "shrug"
would be largely worthless as visual isn't really the primary way we detect and destroy aircraft anymore.
I don't necessarily mean to imply that the military is restricting the tech for competitive reasons; but rather just that E Ink Corporation might be price-anchoring relative to what their biggest customer is willing to pay.
(See also: why "holographic glitter" is so expensive, compared to other metallic glitters. Holo-glitter paint is an effective radar diffuser; and, more obviously, the glitter itself is literally https://en.wikipedia.org/wiki/Chaff_(countermeasure) !)