Almost looks like they went for one big e-ink screen underneath and moved the mechanics out of the way between the keys. The "blueprint" also shows such a rectangle that could be one big screen just behind the changing keys.

I wouldn't order it before not reading a review about how the feel of the probably new mechanics is.

How black is black on backlit e-ink? I'm thinking of an inverted theme, because I don't want a keyboard glowing white all over at night.

It's almost certainly a single display. Mini-caps would be expensive and very difficult to build reliably.

The e-ink displays I've seen aren't brilliant at black. It's usually somewhere between 50% to 75% gray. That may well be enough, but I think a lot of people are going to want to see a production sample before buying.

The contrast on the new displays are much better, the spec for E readers (encarta) displays are more forgiving given the application.

Mini caps would be expensive and also not a good look as each display has an IC driver bonded to the glass substrate so you would have this large border for each key.

I totally would want to get my hands / of fingers on one before selling too.

The keys are made of a specific materail so it acts as a transmissive medium, which is like poor mans fibre optic. The earlier prototypes were CNC'd keys, with injection molding the current design doesn't have the refraction issue you're referring to.

I'm an mech engineer working at Sonder, we have an optics eng who worked on this side.

It's actually much better this way, to prevent its mechanical damage, scratching etc.

It's the early unit, the new design uses a transmissive medium that projects the display imagery to the key surface.