I'm glad I found this thread. I didn't fully understand what they meant in the Xbox One release announcement about Plex Home. Definitely thought they meant fast user switching could be done within the app.
I'm happy using Xbox Live accounts to switch users--I just misunderstood the announcement and kept searching the Xbox One app for a way to switch Plex users (purely out of curiosity).
Still nice that they updated the app to allow non-plexpass accounts (under a Plex Home) to use the app by associating it to an Xbox Live account.