What's inside the box?
Powers That Turn The Rest Of The Mane Six Into Alicorns
Perhaps when Twilight and her friends find the six keys to unlock the box, maybe mysterious powers will shoot out of the box and onto the rest of the Mane Six, making a pair of wings grow on Rarity, one horn each for Rainbow Dash and Fluttershy, and a horn and a pair of wings each for Pinkie Pie and Applejack. I think this is what's inside the box because...think about it. If Twilight has been a princess this long, why not her friends just become princesses out of the blue too?
When the box is unlocked, it will reveal...another box. Now Twilight and her friends have to find either the same amount of keys to open it or find even more keys! Or maybe the box has no keys! *dun dun DUN!* I think this is what's inside the box because it will prompt the Mane Six to work even harder towards a similar goal.
Six keys enter the box, and it opens to reveal...nothing?! I think this is what's inside the box because it will be a great lesson for Twilight and her friends to learn, even while Twilight Sparkle is a princess.
So, what do you think is inside the box?