Apparently the Mi Box 3 (69 dollars)((giggity)) can do most of what the Shield does. It is the size of a wonder bread sandwich and does 4k streaming.
On paper, it checks off all the boxes:http://kodi.wiki/view/Android_hardware
Here is the hard thing for dedicated boxes or old repurposed computers:
Displaying animated custom subtitles over a 10 bit 1080p video.
If you use a DLNA player (maybe the one built in your TV), your DLNA server will have to transcode the file to play it. This means it takes the video stream, renders it, renders the .ass embedded subtitles (custom fonts and screen placement/size/color), overlays it, and then renders it all together.
Most television DLNA apps basically support H264 video + MP3/AAC natively and require the server transcode for anything outside that box (H265, DTS, subtitles, etc).
An early review of the then China-only Mi Box 3:http://www.cnx-software.com/2016/04/18/ ... ed-review/
Basically, when you use a ShieldTV/MiBox, your media servier (Universal Media Server, Plex, whatever) will typically send the data raw to the client (SMPC aka KODI). When you use KODI (or its forks) with DLNA content, the server never does transcoding. It assumes you can just render everything sent. This works great if you can actually render it. Not so great if you can't. 10bit video with animated subtitles will
If you never plan to watch kids shows from Japan, it's really not an issue... Fuckin weeb shit.
If you have an OSX machine with access to your NAS, there is a nice OSX app called "SubMerge" that will create plain H264/MP3 videos with the subtitles pre-rendered and pre-muxed into the video. This helps you create videos that will play as intended on Tablets, Phones, Old Computer, PS3, PS4, Xbox, whatever.
Technically you can do this on a PC with Handbrake, but they make it as fun as self-flagellation. SubMerge is a single task app and it does it's job well. It also has a subtitle downloader embedded so that you can pull and pre-load.