Just a quick question for me and I apologise if it has already been answered, but here goes:
Why am I unable to unlock Dark Iron Dwarves?
I have all the necessary achievements but still no quest at the embassy.
With that being said, I did the rep grind and achievement as a Horde character and then switched over to Alliance to play with some friends. Is this now a case of getting a second character to 120 and doing the 7th Legion rep grind in order to unlock them?
According to the faction change support page, reputation should be converted. For example, Zandalari → Proudmoore, Honorbound → 7th.
One thing that doesn’t convert is achievements. So you may have to do the Alliance Ready for War campaign if you haven’t already.
Hopefully this explains it a little more clearly. You can select Quests & Achievements. Looks like you may have to go through the campaign again.