When it first opened, grey panels lined the walls where future stores would be. It was so creepy and sterile (if spectacular) that the Port Authority hung an enormous American flag inside the vault, spoiling the architect's design but warming up the mood and reminding us that We Are Still At War. The flag disappeared as the mall stores began opening, giant photos of bony fashion models being a good-enough equivalent of Old Glory. Orcs are currently erecting some kind of giant bandshell/kiosk thing inside the vault. If the idea is to have music in there, the acoustics will probably be horrendous. Will keep you posted.
Update: The bandshell/kiosk thing was erected for a Grand Opening event for the Croculus. Some kind of terrible live R&B/jazz/lounge group boomed inaudibly in the interior. If you walked in to hear the music you were greeted with signs saying this was a public event and you consented to any use of your likeness captured by photo or video. People packed under the dome seemed to be enjoying themselves. Food was on sale courtesy of Pret a Manger.
Here they are setting up for the event (via AM NY):