That was very cool!
Now I tell you what I know, which may or may not work:
- on/off switch: the PMIC can be set in shipping mode.
- low power consumption, this below is for the msom, we still miss the data for the Muon as a whole bord:
About this, I want to add that there is a 3V3_AUX that powers the ethernet/LoRa/QWIIC/40 pin connector which can be disabled when going to sleep (or only turned on when needed - example: take a reading of a sensor).
- the Ethernet chip can be set to low power, still consumes 13mA from the datasheet (but killing 3v3_aux might be the way to go)
- ESD protec: no clue
- Fuse: no clue
- persistent memory: the MSoM has an 8 MB flash file system
Like you mentioned, perhaps one alternative is to create a Hat for what is needed, or look into using an already developed hat.
Best,