There was an interesting leak on the interwebz awhile back it briefly talked about the role Andy Serkis will play and his character.
According to the article it's implied that Serkis' character had some association with Palpatine/Sidious pre TPM.
And as far as I recall the only Sith mentioned pre TPM was in episode III at the opera when Palpatine tells Anakin about Darth Plagueis.
"He became so powerful, the only thing he was afraid of was losing his power...which, eventually of course, he did. Unfortunately, he taught his apprentice everything he knew. Then his apprentice killed him in his sleep. Ironic. He could save others from death...but not himself."
So the voice in the first trailer is confirmed to be Serkis, and according to the article I read Serkis plays an ancient alien Sith Lord....that may have some connection to Sidious pre TPM. Based on what Sidious tells Anakin it could be a red herring to lure Anakin closer to the Sith or Darth Plagueis was truly Sidious's master and was "killed" by him in his sleep. But perhaps this ancient evil allowed his apprentice to "kill" him giving himself to the force much like how Obi Wan did in episode IV, because he discovered a way to cheat death and return in another body.
I'm not anti to the idea of Darth Plagueis being the alpha Sith in this trilogy, it would connect the Prequel Trilogy to the Sequel Trilogy but many of the senators at the Galactic Senate are not as keen to the idea. And if Serkis plays some other ancient Sith that's somehow survived in the shadows during all the events of the PT and OT so be it but that is gonna need some real good explanation! Other wise it will just seem like wise ol' Master Yoda made up the Sith Rule of Two.
Now onto Kylo Ren...
he could be an interesting Sith....is he the supposed collector of ancient Sith relics? I hope so because that would lend credence to the cruciform Lightsaber with the unrefined blade and his recently revealed helmet.
As far as the lightsaber I'd accept rudimentary understanding of lightsaber construction or ancient Sith artifact.
The helmet, IMO is too similar to Vaders' especially without the gold highlights which apparently have been removed in the final design. I much rather find out this was an ancient Sith armor design when the Sith Order was at it's Apex and Vader's Helmet was an Updated version of this design. Otherwise it's uninspired and unoriginal IMO.