But I kinda wonder what's the two-part premiere would about. Since Flurry Heart confirmed to be the main character in the two-part premiere, maybe I should give you a theory about it. This blog post was posted on January 29, 2016, so many ideas I came up with would be incorrect.
Plot: Perhaps the summary of the episode would be about that when Flurry Heart was born, she would be the first alicorn baby born in a thousand years (Cadance didn't count, because she's born a Pegasus according a chapter book). So I have a feeling that her magic would be unstable because she have both unicorn magic and pegasus flight (I mean, look at her giant wings and long horn!). Since Flurry is the first alicorn baby born for a long time, perhaps a villain would come to kidnap her to use her power to take over Equestria. This summary I came up with based on a Fairly OddParents episode, Fairy OddBaby.
Villain: Maybe the main villain would be Queen Chrysalis again. Remember she isn't dead yet, according to the IDW Comics (or I could be wrong), so maybe she and her army are going after the baby. And it's up to Twilight and her friends (as well as Starlight Glimmer) to protect Flurry from being kidnap by her, even if she don't know how to use her magic and giant wings at an early age.
But who knows. Let's wait later for the official plot for the premiere.