I'm not absolutely certain, but as I recall the first wave of busts is set to ship in Oct/Nov.
Piggy isn't in the first wave (it is Kermit, Rowlf, Bunsen, and Beeker) or the second (Sam, Gonzo, Statler and Waldorf). Hopefully she'll be in series 3 (my guess is either Piggy or Fozzie will make series 3) and they'll come out quickly. We'll have to wait and see.
Piggy does look great, though, I was really impressed when I first saw the prototype pic.