[ilyt]

> Having said that, even as a hobbyist, I don't see what's wrong with it? Maybe I have written some code that is already running on my Arduino, and I want to add a sensor that is only available for RPi, without having to hop onto another platform... nothing wrong with that.

...use a piece of wire ? None of the interfaces are fast enough to need a breakout board.

It's not "all arduino to rPi hats" adapters either (which would be far more useful tbh), it's "that special expensive ARM stick from arduino to rPi hats".