At one point I stuffed 40 of them into a rack mount and built a cluster to use for teaching at my university. Never gotten any publication out because it‘s fairly uninteresting from an academic point of view, but as a teaching tool to learn ARM assembler or parallel programming / how to execute stuff on supercomputers / OpenMPI it’s an invaluable tool.
Recently there have been some odroid c2 added to the cluster, so it‘s not only RPis anymore.
More info: https://www.caps.in.tum.de/en/himmuc/
Some Beautyshots at my Instagram: https://www.instagram.com/p/BcA1QdFgWuk/