The Surface pro is fanless and pretty powerful
I like the idea of a more-or-less dedicated box running Renoise and using assorted custom controllers designed to make manipulation Renoise easy and intuitive in a live setting.
I'm currently working on some software that works as a MIDI-to-OSC proxy, with some custom tools managing track/pattern manipulation.
I'm using an Akai MPK MkII mini, and noticing that a smaller controller with just some rotaries and pads would work better (smaller footprint).
Building such things with arduino/teensy/etc would be pretty straightforward. (I probably already have the parts.) My use case doesn't need velocity measurement so the MkII mini is overkill.
Custom PCBs + surface-mounting seem like overkill, but maybe if I knew how to do all (and had the right tools) that I'd think otherwise