It looks like Hasbro has decided to start releasing 5 inch pony plushies. These in particular were found in a recent shipment at a Target in Alaska. The box is saying a release date of July 29th, so we have a bit of time before they become officially available.
Only Pinkie, Rainbow and Twilight have been seen so far.
Thanks to Cluchey for the heads up!
Have some new individual images: