I don't know…
Back in August Jayson Thiessen did a question/answer thing where he said that he likes Trixie and believes that there is more to tell with her.
(WHOLE THING IS HERE)
Now that could be an off-hand comment or a subtle hint at the future.
Personally I would love to see Trixie return for revenge.
She clearly didn't learn her lesson in Boast Busters given her exit, so I think it would be funny to have her come back to try take Twilight down a peg.
(My true dream would be to have Trixie be MLP's version of Sideshow Bob, showing up maybe once a season with some new, increasingly crazy plans for vengeance, but I'll gladly live with a single episode, too.)

Nah, I'm just screwing with you.