There we have indeed, Plex running on my Xbox One.
I’m pleased to announce that the server was updated quick as lightning and is now compatible with the new Xbox applications.
Enjoy!
The official blog post at Plex.tv can be read here https://blog.plex.tv/2014/10/05/plex-xbox-one-xbox-360/
EDIT: I forgot to mention that this currently is only applicable to PlexPass users.