I've been thinking of doing something with Octavo parts, because my electronic design skills are totally obsolete now and they are simple to integrate. My idea is a board with 16 parts (for 32 cores) with red LEDs lining up one side mimicking a Thinking Machines CM-1 cube. Not a CM-1, but a lot of nodes if you join 16 boards per cube.

Are they selling a service of, like, building a multi-chip package where you pick the chiplets? That seems crazy futuristic.

No. They sell bundled parts where they integrate SoC, memory and passives so that you can just connect power lines, an SD card, and start running it.