My impression is that their metasurface lens has approximately a 1 mm focal-length. In the diagram, the light appears to pass through an intermediate focus at that distance, which they then pick up with another optical system for control/convenience.

I don't see anything that would, in principle, prevent using the metasurface lens as a component of a tiny camera. Nature has certainly evolved imaging systems that are smaller and modern sensor technology permits wavelength-scale pixels. With maximum charity, it appears that this lens/methodology might be used to yield a ~1-2 Mpx imaging system with a 1 mm f/2 optical system.

The claimed advance here appears to be that the combination of their lens and processing yields higher quality imaging at these physical scales than prior work.

It does indeed appear that in combination with a tiny imaging sensor, this lens could yield a camera the size of a large salt-grain.

This entire field of engineering appears to be in a golden decade; it may not be too long before we start seeing metasurface optics in consumer imaging products.

[1] https://www.etymonline.com/word/camera

Not necessarily. I recently looked into miniature cameras for self- built drones.

For less than $50, you can get a package with a lens that's maybe 2-3mm across. The entire sensor+lens unit is roughly 1cm cubed. But then you need the electronics to process and store the image, and you're up to credit card size. And then you need a battery, and not a tiny one because that image processing draws quite a bit of juice.

OTOH the light sensor needs not be as small. Imagine a thin optical fiber with such a lens on one end, and a large lens and large enough camera on the other end. In could immediately make a better and less invasive endoscope, e.g. for surgery.