What do those things go in anymore? Surely there are asic pid controllers that are insanely cheap? Tuning an analog one I can see probably doesn't make sense anymore, but there is something nice about being able to do that with a screwdriver instead of jtag. What do these M0s go into?

I used an 8-bit PIC micro a couple years ago for power applications (think non-IoT lighting). The specific microcontroller we used had nice peripherals for sensing, and controlling diodes, but no FPU. I remember looking into getting something external to handle the PID, but the cost and board layout constraints made it challenging.

It’s changing rapidly. I can get $0.10 32-but microcontrollers that run at 48MHz and handle plenty of soft float operations just fine.