Here's what I hope to see in Season 4:

-The Manehatten Branch of the CMC

-Rainbow Dash/Wonderbolts arc continues

-Scootalove

-Rarity's fashion career goes somewhere

-Twilight being an adorkable alicorn

-Fluttershy being awesome using the powers of kindness

But I think the real reason why I'm so excited for season 4 even more than I was for season 3, is because season 3 marked the end of an era. What I call the "Pre-Twilicorn Era" is now complete, and season 4 will be the beginning of a brand new story arc. That's incredibly exciting.