I'm thinking about building one, but with Pi Zero's and USB networking. The ClusterHAT guy wrote software to netboot the nodes off a cluster controller's SD through the USB network. With that, you don't even need an SDcard for each node.

I was thinking about also adding a LED bar with one LED for each GPU SIMD element, refreshing a couple times per second and lighting up for the units used above a certain threshold. The ARMv6 SIMD instructions don't look that encouraging.

The end result would be something that looks like a small Connection Machine.