Not sure if discussed yet, but that scene with the supposedly Sith guy appears as if he is looking for something, and when he activates the saber he seems to be looking downward. Then considering the whole "grave digger" thing and that this character has been collecting ancient sith artifacts. What if the saber crackling isn't because it's a DIY saber, but the ancient saber of whoever it is he's trying to resurrect? Perhaps he has made it to the entrance of a tomb and is using the saber to cut through it? Then when he resurrects the dude he hands him his saber.
That would then go along with the theory that it is Han's son, because he wouldn't actually be a Sith at that point, just an artifact collector. The way he appeared in the trailer didn't exactly come off as a highly skilled Sith either.