The unrooting steps were writen when very little was added to make a device rooted...
Now Much more is detected as root changes including scripts and other stuff intell CPU android boxes needed over ARM CPU units... So nuking those scripts is a lot harder...
Even google play store rejects many downloads to android boxes...
Even if you get past the Root error you may hit a "HDMI is not supported" error if the box is upscaling to 1080p...
Native 1080p out put can by pass that...
So custom android Boxes are not supported...
Next year when Chrome OS is dumped by google for Google Android Desktop that may change... as android N will have native HDMI only devices from google...
Ooooo desktop mode features in developement...