Don't hold your breath. Believe me, I love Derpy as much as anybrony. But given the broohahaha that happened after Last Roundup, I doubt she will ever speak again.
As much as I love Derpy arts, stuff like this makes me nervous. I can hear the faint echos and rumblings of Derpygate. The insane overreaction to the edit from some quarters of the fandom made us all look bad and I'd hate to see that happen again.
At least right now Hasbro is still allowing her the merch. And she's in at least the first issue of the comic.
She did, but not VERY well. She's a clone in the stands of the Magic Duel performance at the end, the opposite stands. You would have to look very hard for her though, because it's dark. Also I think the back of her head in Too Many Pinkie Pies somewhere. A lot of bronies are just butthurt because they feel entitled to have whatever fanon they want on the actual canon show. I loved Derpy's appearances, but I don't "miss" her. She still shows up in the intro and she was never pulled from the show. She still exists, and that's enough for me.