Let us play with the thought of Blizzard planning a new world boss, a new dungeon, hell even a new raid(!) without having it on ptr! Imagine the "WoW brand new feeling about it all". Would that even be possible these days?
This is game has been around for quite some time now, and for most players it has somewhat lost the feeling exploration and shining new sparkle. So would this be an idea you would think Blizzard would even consider?