It’s almost like major delays happened and not all content made it in SL.
But Blizz has always confirmed the rest of the heritage will happen and they were working on it. I’d strongly assume the remaining seven sets will be throughout the next expansion.
It also makes more sense too because the core races have small story arcs tied to theirs. Which is easier to do when we’re back on Azeroth. That set in the image is not the heritage armor. Iconic as it is, it’s just NPC gear Blizz used for the Darkshore invasion. I think the real armor would be something more new that we haven’t seen before, instead of being lazy and reusing an old set.