My guess is we will never see a forsaken heritage armour, given the path that they have taken Slyvanas and the Forsaken in recent times
We will definitely see heritage armor for every race, but it's far less pressing to have human, orcish, night elf, or forsaken armor since we have had battlegrounds with racial themed armor recently. Worgen and goblins were the natural next choice. I am betting either draenei or night elves (since the latter is playing a huge role in the story right now) and either trolls or undead (same as for night elves) will be featured next. Humans and orcs will almost certainly be dead last. And that's okay. They have tons of racial armor readily available.
That said, the night elf armor is basically already available... it seems like a waste to not just use it. I am guessing Blizzard isn't read to have the night elf heritage armor quest yet. It may follow up on Malfurion and/or Tyrande's story, which is stagnating until the issue with Sylvanas is resolved. Same for Forsaken, coincidentally, for the same reason.