Guys, save yourself the aggravation and just get another device for 4k playback. I bought a Firestick 4k with the LAN adapter and have not looked back. I WANTED my Xbox to be the one device for all media and games but I doubt it's going to happen. (Its been how long waiting on this?) Save the XBOX for games and maybe DVD / Blu-Ray playback.
Not exactly the best solution, but yeah I get ya. I went over to plex, plugins are crap and the only 1 I want does not work but it's free and plays 4k. Emby was much better with remote streaming, probably to do with all the ports and hacks needed to get it working behind my reverse proxy.
Would much rather pay Emby but no point if half my media does not play.