On Fri Jun 11 15:29:35 BST 2021, I wrote:

This looks like another interesting reuse of an existing connector:

https://learn.sparkfun.com/tutorials/getting-started-with-micromod

Not quite at the System on a Chip level hardware, but still useful for certain applications, I'm sure.

I bought a couple of processor boards and a carrier board to see how well it worked and it seems fairly easy to get going with. It would be interesting to see a low end SoC processor card. Maybe someone with PCB design skills could prototype one - it would be interesting to see what could be done with it.

David