If you're asking yourself "what's the point in building another little ARM cluster?" I can totally relate.  Answering questions like that is actually what motivated me to begin this project.  I've thought about this a lot and written a bit about it here:

https://jjg.2soc.net/2017/12/13/why-personal-supercomputers/

This post is a little behind the current state of the project and I've refined my ideas a bit since then, but I think it does a good job of explaining my motivation behind creating the RAIN project and the multiple vectors I'm exploring.