According to Indie Revolver on Saturday, sources indicate that a main villain from previous "Star Wars" films could make his way into both "Star Wars 7" as wall as "Star Wars 8." There had been a picture going around online with a Sith-like being holding Darth Vaders damaged helmet that was thought to be such a villain, but turns out it was just likely a Sith Inquisitor that is synonymous with the non-canon story line. The new "Star Wars Rebels" has such a character. Keep in mind there is nothing official about this information.
It seems sources indicate that Emporer Palpatine may likely be the main mastermind behind both of the upcoming sequels and Ian McDiarmid is reportedly not to return as the actor portraying the villain. The picture in question where said possible Sith Inquisitor is holding Vader's helmet.
This may be only be speculated as one or multiple inquisitors, that if the emperor survived the fall from the pupil that betrayed him, could very well put together Palpatine in the same fashion that he had done so with Anakin. It appears when one suffers major injuries in the "Star Wars" universe, robotic enhancements seem to be a popular replacement of limbs and other such things.
Palpatine could have been thought to be laying low this entire time after the defeat of the second Death Star and "pulling the strings" by taking on someone else as an apprentice to do his dirty work. A non-canon Sith Inquistor would seem to be a likely candidate for such an apprentice position.
J.J. Abrams' "Star Wars 7" film is scheduled to be released come Dec. 18, 2015.