She looks so sad. But then, it's in character for her. More power and responsibility, more to worry about getting right, and we know she just wants to be seen as a normal pony, though that ship has long since sailed. I bet the first pony to swear by her name like they do with Celestia within her earshot gets kicked.
Awwww yeah! ALL HAIL PRINCESS SPARKLE!! This probably means she might get her own empire, the Sparkle Empire! I wonder what the ponies there would look like? i imagine them just glowing all purple and dark pink (even their pupils as well), that would looks awesome ^_^
And maybe if twilight is the princess of friendship that means all of her friends souls belong to her or I guess she could be princess of her library. I can't be the only one that would like to see her turn the treehouse into a castle am I?