Not sure if its been posted yet, but you can join a friend on another realm in a party and it should phase and work for you. The person you join needs to be 90 is all i can confirm, My realm was Aman'thul and the realm i joined was Khaz'goroth if thats any help.
This quest works on Shattered Halls-US as intended. I grouped with a player from Wildhammer-US last night and escorted him to the quest hub so he could complete it (and did). It seems to be broken on many realms from what I've read, but it does work on a handful and through cross realm grouping.
If this isn't fixed with today's maintenance, I'm going to be pretty disappointed. Once bugged, you can't complete the Halls dailies that require killing mobs inside, unless you group with someone who is willing to just kill it and give you credit.
I can confirm that it got fixed, I managed to do my quest without any problems.
Hotfixed yesterday. See front page hotfix notes.
Humans are the only species on the planet smart enough to be this stupid.