I think the fact that Buster Prime wasn't released as the first Movie Masterpiece suggests that they heard the Buster Prime feedback; that many people considered it Masterpiece level, and based on that, they're simply testing how Starscream will sell with different marketing/box.

It's the end of the line pretty much, they've got nothing to lose, and if it pans out we may see dedicated Movie Masterpieces down the track.