If you look closely, you will notice that both nacelle pylons also have windows on them - 3 on each pylon, to be exact. The port-to-starboard width of these pylons is about the same as the port-to-starboard width of the neck. It's hard to argue there's any habitable space in the nacelle pylons, other than a maintenance crawlway that leads from engineering up to the nacelles. Yet, like the neck, it has windows which could suggest lighted maintenance alcoves.
I would suspect the innards of the neck to be similar in nature to the interior of the nacelle pylons, only on a larger scale.