> Or roll my own, but I've tried that and found it pretty difficult.

I agree, there seem to be no good options for this. You can use Kodi or whatever, but I want something that supports playing my ... totally legally acquired content... and Netflix/Disney/iPlayer/etc. In a package that's silent and low power.

Doesn't seem to exist unfortunately. I guess the closest is Nvidia Shield. You can apparently still sideload APKs onto that... for now. I'll buy one when they release an update. I'm patient!