"On the longest day of the thousandth year, the stars will aid in her escape". You noticed Twilight Sparkle´s cutie mark? Stars. Wait, but she didn't help Nightmare Moon in escaping from the Moon, right? However, being Nightmare Moon was a prison for Luna. Therefore, stars (Twilight Sparkle) helped her escape her prison.
There's also a Stealth Pun in that the stars, the Mane Six, help release Luna from Nightmare Moon.
A bit of Foreshadowing happening in the fact that Twilight's element is a sort of crown instead of a necklace, because it's her first step to becoming a princess.
