It appears that the Uniques that had a chance to drop from Dungeon Bosses have been merged with the new Dropped Set items. Same it seems with some quest rewards that offered Uniques.
I have noticed that I get a Unique named Leg Armor from a certain delve, but it is always the same dropped set and trait. I get this item about every 6 to 10 kills.
So, its just another way to make sure we always get that Dropped Set item from a Dungeon Boss, but still have a chance to get a Unique item like we did before.