The most likely rotations would be Boundaries Crossed-on or Plasma Storm-on. I would think anything from Plasma Freeze onward (Plasma Freeze, Plasma Blast, Legendary Treasures, XY, Flashfire) would be safe to get. If you want to be completely safe, XY and Flasfire are guaranteed to stay in format, since they're so new, though I truly cannot imagine that Legendary Treasures or Plasma Blast would rotate.