Oops! I didn't know it had already been posted. I don't see how the substrate matters (though I know nothing of this kind of physics). It would seem the problem would be placing the right sized antennae evenly. And one size of antennae for each frequency of the visible spectrum. I would have thought the substrate would be transparent to a wide spectrum of electromagnetic frequencies.
In the mid-sixties, I read an article in Scientific American about the possibility of guiding droplets of ink to precise placement on paper. I have now owned at least three generations of ink jet printers. However, if these lens take as long to solve the engineering problems, by the time they get to market I won't be around to marvel at them.