It's a very interesting technology, especially since it holds the promise to directly realize an almost arbitrary phase-mask (analogous to a lens' shape) that h

It's a very interesting technology, especially since it holds the promise to directly realize an almost arbitrary phase-mask (analogous to a lens' shape) that has been found using already existing optical design technologies. The problem, as in the article is size though. Apart from the optical (especially on-chip) applications, in theory, it's possible to have a freeform surface and cover it with small meta-atoms (subwavelength structures) so that reflected wave-fronts are planar again, like the incoming one. With millimeter waves such structures are way easier to make than on the tens-of-nanometer scale - these will be used in all kinds of aerospace products. And iirc, the first application (according to Frederico Capasso) was laser optics on a satellite that had to be compacted and have their weight reduced.