Plex does not and will not support the Xbox platform. As there seems to be a lack of clarity on this issue I'm providing clarity here.
If the Xbox platform was at all a priority for Plex they would support it. They do not. If you wish to use Plex on a supported client please choose a platform such as Android or Roku.
As the Plex business grows and it's ecosystem matures hopefully they will make a change to adpot a 'grown up' approach to road mapping and customer communication rather then simply abandoning platforms with tens of millions of users and never letting anyone know what's going on with them. You're not a young little startup anymore Plex, it may be time to consider acting like a big boy now.