Found this while messing around with some stuff.
People can still see you, carefull when going through walls or jumping from chair to chair.
Screenshot by Lightshot
Requirements:
You need have done the Theramore scenario so the crater appears instead of the old theramore isle.
you need to go to this npc: Zidormi - NPC - World of Warcraft and get this buff Time Travelling - Spell - World of Warcraft
after that simply head to theramore isle and enjoy the fun.