Hello,
I just got a Pi-Destop from a friend as he had no more use for it. It makes use of a RPi 3. I installed LibreELEC as I'd like to use it as a media station.
After tinkering a whole day I managed to get the power button working.
The original scripts make use of the RPi python module which was dropped by LibreELEC, for some reason. But I managed to rewrite it with the help of Pi-Desktops pin documentation, their state machine and their scripts. I'll be making a tutorial with a scripts that will setup all the required files but you'll still need to install the Pi Tools addon. Once I polish it enough I'll post a link to all the files.