The original note, as written at the time
Here is an alternative way to design a cleanable keyboard. Make sure the buttons are rounded like little heels from the upper surface of the keyboard. This will ensure a sectional profile where the button always has a surface that makes it easy for you to reach between the buttons and clean efficiently.
Ongoing development
An alternative cleanable keyboard: make the buttons rounded like little heels rising from the upper surface, so that the profile always presents a surface you can reach between to clean efficiently.
The detail is the profile, and it is the right place to look. A flat key sits in a well, and the well is where crumbs, dust and grease collect in a place no cloth can reach. The gap between two flat keys is a crevice with three walls.
A rounded button on a smooth deck is a different geometry. There is no well; the gap is a valley with a continuous floor, and a cloth pressed down goes into it. The heel shape — narrow at the top, flaring at the base — gives a fillet that a finger can wipe through.
The honest trade is typing feel. Flat keys with a well are easy to make consistent and cheap to mould; rounded keys need more precision and a different mechanism, and they can feel vague under the finger.
The other gain is that a rounded deck can be wiped as one surface. Anything that lets a keyboard be cleaned in ten seconds with a single cloth — rather than ninety seconds with a brush and air — is a device that will actually be kept clean.
That is the real measure. Not how clean it can get, but how often somebody bothers.
Design for the ten-second clean.