If you want something useful, you should add udev rule:
SUBSYSTEM=="input", KERNEL=="event*", ATTRS{name}=="sunxi-gpiokey", TAG+="power-switch"
However, this will shutdown your board, because it sends KEY_POWER. I think kernel patch is needed if you want to change it to KEY_SLEEP. Waking from suspend should work flawlessy now on Armbian.
I reorganized all patches in OpenELEC and kernel configuration so the kernels are more similar now. I still have CMA/kswapd issue, but I still have one idea what to change. In the process, I found the reason why suspend on OpenELEC doesn't work. It works when CMA is enabled
Nice progress in unifying all the images. Did you consider porting MMC driver from mainline kernel to solve the issues?