Handed in my 16 Nerubar Finery for the quest to gain the stacking raid buff. The quest reward was simply 75 kej, no other indication of a reward. The tooltip for the raid buff still says “0% increased damage and healing”, which I confirmed isn’t a tooltip error - abilities do the same damage/healing inside and outside of the raid.
Can’t see anyone else reporting it yet, but others in the raid group i was in also have not received an increase on their buff.