> The unfortunate part is that CoreELEC only works when you get all your content from a locally attached disk. You can't even really stream it from your beefy NAS/server

This is not true. Streaming from a NAS at high speeds is fully supported and works fine. I would suggest to use NFS over SMB though, SMB gives me issues for higher bitrate content

Streaming apps do indeed not work. It's a device for local / NAS media playback.