Here is another Google spreadsheet table of millicomputing module specifications.
There are several approaches, but some of these are edge connector based, include on-board ethernet, and could be stacked on a motherboard in a very dense array.
I think that on a standard 1U motherboard, if we could get five rows of 24 connectors that is 120 individual modules, using less than 100W maximum. The motherboard would just need to provide power and ethernet switch chips. If we also want per node storage, there are many very dense NAND flash ships in the multi-Gigabyte range that could be added to the design.
So is that interesting? I think so...