The Priest Class Halls are guessed to be Karabor and the Naaru Spaceship - Naaru Lightshift, amougst others, but it remains unconfirmed for now. The images below appeared after the alpha was opened, and they excited me so much that I decided to share them with you, just in case. I also managed to find a video, which is at the end of this post.
The building starts with a entrance hall which leads into a round blue room, with two small corners on either side as you enter, and a podium in the back. On the left is the entrance to a round purple room, and on the right an entrance to a round yellow room. At the bottom of this post is an overview image of the entire building.
The location is visibly a draenei structure, reminiscent of Tempest Keep and the Warlords of Draenor cities Shattrath and Auchindoun. It has those nice purple, blue and yellow colors in the design, possibly representative of the 3 priest specs, maybe we'll be lucky...
If this becomes the priest class halls, it would be filled up with NPCs and objects, but the empty space is already very impressive. You can take a look for yourself in the video below.
Source missing for images. Uploaded to imgur and shared by a guildie.