This looks awesome!

This looks super cool. Definitely on my "I want one, but have no idea what I'd use it for," list. The idea of clustering Pis is really interesting, but for me anyway it's in the "solution looking for a problem" category, though most of my projects are.

Any idea what you'd run on them, Jason?

valorum,
Probably just a file server or a web server for my personal data and web page, nothing special.

I've got a bunch of various microcontrollers/Soc and they are pretty fun.

One project I've wanted to work on is getting pianoteq on a RPi 4.
Pianoteq is different from a synthesizer in that it doesn't used pre-recorded sample but rather a mathematical model to create the piano tone. It is much more real sounding.

Pi4 + a DAC from hifi berry + keyboard (ie Roland A-88) is a great way to go rather than spending much more.