The promotional image features a property dubbed "Equestria Girls: Legend of Everfree". This would be the first instance we've seen an upcoming project bearing this title, and confirms that the Equestria Girls series will not be ending with a trilogy. Of note, is the fact that as-of yet, the third installment of the films - Friendship Games - seems to be entirely direct-to-DVD (and BluRay), unlike its two predecessors.
Shortly before this image was released, a mysterious job posting appeared at Hasbro, seeking a "Franchise Creative Lead" for a My Little Pony property, a position that was filled almost instantly. This would lead some to believe that the position was likely filled internally.
Now, knowing all that information, one must only look at why Equestria Girls exists in the first place to get an idea what could be happening here.
Equestria Girls is Hasbro's response to their competitor Mattel's insanely popular line of toys/money printing machines "Monster High" who just last year became partnered with Universal fuckin Studios. (You'll remember earlier how Hasbro was considering merging with Dreamworks....what a strange coincidence...)
You may be shocked to learn that Monster High, since its creation just 5 years ago, has released not 1 or 2, not 5 or 6, but 11 GODFORSAKEN FILMS in that time. (Thats more than 2 movies per year)
Hasbro, clearly needs to up their direct-to-video game if they want to have any hope to compete with the original multi-colored-goth-girls.
And they are, as this "Legend of Everfree" indicates.
Engaging the speculatron, it seems as if Hasbro is poised to get a dedicated staff for the Equestria Girls franchise and start pumping out Blu Rays and DVDs faster than you can say "muh headcanon". Why would you sink the money into founding your own shiny brand new Allspark Studios if you don't plan to USE it?
After Friendship Games. All the pieces will likely be in place for a whole new world of neverending human adventures with the new mane-7 featuring Sunset Shimmer as the mentor and Sci Twi learning about friendship.
All coming soon to BluRay and DVD at a store near you.
God please don't let me be right.
Now, this is naturally all speculation.
All these pieces could be completely unrelated, and Hasbro may have no competitive business sense whatsoever.
But if the collossal Equestria Girls boot fits...