"Developer mode" is incredibly brittle. If you don't press the right key combination at boot, your user partitions get formatted without warning and you lose all data. That makes it essentially a toy, not a real "developer" device.

I see your point, but it's not as bad as that. Pressing the right key combination is optional, and all it does is skip an annoying beep. Factory reset isn't triggered by inactivity, it's triggered by pressing space and then confirming.

It may have changed in the past two years, but there was a 30 second splash screen saying "Press space to continue". If you press space during that time, it will "continue" to safe mode, wiping your entire crouton environment. There was no indication at all as to the key combination needed to skip the 30 second wait time.

You have to also confirm clearing data with enter after pressing space.

Has anyone stuck a Teensy or arduino or something inside of a Chromebook to automatically send the right key combo? Seems fairly simple to me to do, but I don't have a Chrome device to test that on.

If you're opening up and messing with the hardware, why not remove the write protect and flash the firmware instead?

...Or completely replace the innards with a Raspberry Pi Zero W. (Not sure if it’s actually possible.)

Various pi boards have been retrofitted into laptops but a Pi Zero in particular is a downgrade in performance from just about any relatively recent laptop/Chromebook. As some of the sibling comments mention, there is more involved with resetting than an accidental non-action during boot.

Even better you can switch to coreboot and load Linux, there's even a Chromebook-specific distro, https://galliumos.org/

You can even just boot Linux, or dual boot.