I'd like to see Gilda again.
And as much as this is unlikely, a Derpy and/or Dr. Whooves scene (or episode!). That would make my life complete. Mark my words season four will be a great season, there's so much to look forward to. I have my hopes that they'll show new cultures or species living in that world.
Spoiler for people who have not seen the Bronycon preview clip. Anyways, us learning about Equestria's past with Luna as well as Scoot-a-loo's trouble with flying episodes are the ones I am looking forward to the most. I think this once again shows that the writers do listen to what the fans want.