[Orothrim]

Have you considered any of the raspberry pi power button options that exist? Something with a reasonable size capacitor and a signal pin to let the Pi know to shutdown when it's lost power, before the capacitor runs out, might work?

[somewhereoutth]

Yes capacitor power button would work (assuming it is reliable). Still an amount of faff and expense to set up, especially if you are scaling a deployment. It would be great if the RPi (or some version of it) had this 'pre-installed'.