A player has discovered the location of GM Island in MoP Remix using the Warband and the Kalimdor scouting map.
When you use the 
The Warband Map to Everywhere All At Once and then use the 
Scouting Map: Surviving Kalimdor in MoP Remix, you’ll discover GM Island as a location, as pointed out by Reddit user Mechygyrasaur.
According to Dovah the Explorer, Blizzard has removed GM Island from the WDT files back in Patch 8.2. Although the map files for GM Island are still being shipped, the removal from the WDT means it won’t load without client modifications, such as model editing.
GM Island is being removed in 8.2
byu/AKDovah inhiddenwow