Dalaran Island is an empty subzone of Dalaran that can be discovered by flying high above the city. It is not considered to be part of the no-fly zone.
Dalaran Island is possibly an older version of Dalaran.
Dalaran Island seems like a vestigial leftover from a WotLK alpha build.
Dalaran Island may be another name for Cross Island.
Dalaran Island may be the rock that Dalaran proper is resting on.