Amazon.com briefly had an image up from the upcoming My Little Ponies/Transformers crossover 2015 MLP Specials G4 Brushables toy line. It has since been taken down, but not before my spouse was able to grab an image of Bumblebee and Optimus Prime as Ponies:
As we can see, it uses the G4 Ponies designs and seems likely to be linked to the upcoming comic-book crossover from IDW in a bit of cross-promotion. I have no other information about this at this time. The Amazon uk site where the image come from now shows the Ghostbusters Ponies.