For those of you who are not very far along with this grind, make use of the BC Timewalking event
and start the quest chain starting with 友善
on one of your alts. I just tried it and can confirm that the 50% rep bonus applies and instead of boosting you to normal, completing 灵翼之盟
gets you straight to revered
(+63 000 rep). I didn't see this information anywhere else so I thought I'd share, hope it helps.