You do realize that the books are not part of the canon, and therefore will never be used in writing the story line for any of the movies? These factions took place before the rule of 2, and besides what took place in the TV series The Clone Wars, there has only been 2 sith since. What I actually hope we find out is that Rey turns out to be the actual chosen one, not Anakin or Luke, and actually brings complete balance to the force.