Had to dig out this post from an earlier page as I think it tells us quite alot, bolding is mine. I think it tells us that Hasbro had always planned to release the third sister but realised that they shot themselves in the foot with the designs for the first two limiting their options. Most seem to agree that the concept art presents a horrid mess for the combined form and I reckon that Hasbro came back to this and didn't give the original a pass. I expect that they have gone back to the drawing board for No.3 and are trying to rework the design in to something that could just about complete the combiner without being a total howling failure in the fans eyes. I'd still like to see something decent come out of this, the original concept is quite daring but I think it may well have been the project that kept being sidelined, passed around and restarted internally and still may never see the light of day.