[chairwizz]

Does anyone know if the Shield has access to Android's night mode for filtering blue light?  As a lesser option I take it that the twilight app can be installed?

No, because the Shield runs Android TV not mobile Android. Whether you can install the Twilight app or not I can't say, you can try sideloading it but that doesn't mean it will work.

Can the Shield be rooted in order to install f.lux?  I'm guessing that rooting would mess with access to HD Prime/Netflix though.

  
Yes you can root the Shield. Nvidia provides pre-rooted FW that you can flash. No it doesn't do anything to Prime/Netflix, they'll work just as they would on an unrooted Shield.

Thanks! That sounds promising re: rooting, I’ll go look into that.