My dream device for clustering is dual core 1Ghz+, 1GB ddr4 (ddr3 in a pinch) and wired Gb ethernet. In bulk (where bulk ~ 100) price $5-10. Some of the allwinner and rockchip based pi clones get close but price is a lot more.
For qty 1 @ $30 you get 2GB and 4 cores, you could put 2 more ethernet ports on the PCIe port for a total of 3. That gets you into the same-ish performance regime.
I am all for aggregates of low end compute, but I think something with more processing power and more PCIe lanes would scale better.
