For a while now, Amazon has had a DVD listed as "My Little Pony Friendship is Magic: April". The information on it is your typical generic pony summary without an episode list.
Someone going by the name of Sebastian tossed the UPC into Google, and found a bunch of other locations carrying the disc. While the information is still generic, they all drop a specific "Twilight Sparkle Princess" title. How ominous!
I guess only time will tell what exactly is on it. Have some links after the break of various locations that will have the DVD in stock!