Why do you want LibreELEC so much? That's just a frontend for Kodi. The Nvidia Shield TV has the best software support, no need to try S912 boxes with unknown or bad support.
What's your use case scenario? Netflix, Amazon Video, stored files...?
The reason why I want LibreElec is becuase of Kodi and the ability to passthrough dts audio. A while ago I had difficulties finding a device that was able to do that smoothly, until I got the Wetec Core and LibreElec.
My use case scenario is mostly stored files (1080p high quality) and PLEX (locally).
I use my LG Smart TV for Netflix and Chromecast for YouTube.
I have no problem combining all these use case scenario in one powerful box.
The thing that attracts me the most to S9 devices is because they have a spdif optical output (for dts passthrough). My receiver doesn't support HDMI.
If the Nvidia Shield can meet all the demands above, I will buy one right now!