Hi,
has anyone seen a Raspberry Pi HAT (similar to this one https://blog.protoneer.co.nz/raspberry-pi-cnc-board-hat/) that is supported by Octoprint?
That would be neat for newly built DIY printers, for existing printers w/ a broken motor controller board or for printers where a smoothieboard plus a raspberry pi board are too large in space.
So that specific Pi Hat looks like an arduino nano (or similar) and 3 stepper drivers. I haven't personally seen anything like that, but in theory you could flash marlin on the arduino side (if it fits) and be able to control 3 axes. Unfortunately, you need at least 4 for a printer and enstops/thermistorsm etc. Neat idea though for a compact integrated solution. I did find this project...
This is interesting, but the question is why do it, or what advantage would this have at all over current method, and if the effort worth it. I can't think of any advantage that a hat (connecting via GPIO) would have vs. connecting via serial/USB-to-serial.
...other than losing the serial cable and a source of induced noise in the communication line.
meh... nothing that good quality cables can't solve 
is the best solution when you want to use klipper an octoprint.