A very nice easter egg/secret area has been found in the Nighthold raid, reached by dropping down in specific spots from the top of the raid after killing Gul'dan. There are some very neat touches in there, including a cake and chess models. The room isn't accessible by gliding in from the outside works as the doors are closed on both sides.
Maybe there will eventually be a World Quest in here, or even an actual story quest somewhere down the line, but for now it's just a nice addition to add some depth and reality to the Suramar palace/Nighthold.
Source: Reddit