5 things I expect to see in Star Wars: The Last Jedi (2017) - Part I: Rey's heritage and Snoke's greater scheme are all intertwined
With the recent release of the latest Star Wars: The Last Jedi trailer (watch it here, if you haven't already) lots of speculation has started about the story and eventual outcome of things, since the trailer itself really doesn't reveal an awful lot about its story and looks to be filled with some deliberate confusing and altered scenes that probably aren't going to play out the way as depicted in the trailer.
So all we can do for now is speculate, which is one of the more fun things, leading up to one of the most anticipated movies of 2017. A perfect opportunity to share my 2 cents about the upcoming Rian Johnson movie as well, but please take it with a grain of salt, since my guesses and interpretations of the movie and trailer are of course just as good (or bad and crazy) as yours.
Rey's heritage and Snoke's greater scheme are all intertwined
One of the most talked- and debated about things from "Star Wars: Episode VII - The Force Awakens"; who are Rey's parents and how did she ended up on Jakku? There are lots of theories and thought floating around on the internet already, ranging from 'she's a Skywalker' or Obi Wan's daughter/granddaughter to 'she's a descendant of Palpatine' or Leia's 'secret' second child. In my opinion any of those reveals would be pretty lame, as its something a lot of people expect and a cliché, started by "Star Wars: Episode V - The Empire Strikes Back", that has been done to death. Not everybody should have to be related or connected to everybody in a movie and it probably won't be much of a shock surprise.
Rey is not only the new Luke Skywalker of the Star Wars saga, but the new Anakin as well. Someone who struggles with both the good and light side inside of her, constantly questioning her own motives and purpose. She could be the new 'chosen one', who is supposed to bring balance to the force, much like Anakin. It therefore also wouldn't surprise me if her birth was a virgin birth as well, just like Anakin's was. And just like Shmi Skywalker was a throwaway character, so are Rey's parents. The more interesting question therefore is; 'who planted the seed', so to speak. Maybe the force ghosts somehow found a way to do this, maybe some ancient, thus far unknown Jedi, or yes, maybe Snoke is the responsible one, which probably is my favorite theory.
One of the biggest hints to me is the flashback scene in "Star Wars: Episode VII - The Force Awakens", after Rey touches Anakin's/Luke's lightsaber. Rey, filled with questions about both her past and future, sees not only the things that happened to the past owners of the lightsaber, but of her own past and future as well. We see Kylo Ren and the knights of Ren, presumably after they destroyed Luke's Jedi temple and killed all of the students. We also see Kylo saving Rey from being killed by one of his owns knights. This implies that Kylo, a former student of Luke, knows Rey, as also gets implied throughout other moments during "Star Wars: Episode VII - The Force Awakens". This is important

This theory would also suggest that Luke and Rey knew each other from the past and Rey indeed could have been one of Luke's Padawans at some points. It also would explain why Rey would be able to use certain force abilities already in "Star Wars: Episode VII - The Force Awakens", such as mindtricks and the force pull. So why doesn't Rey remember her own past? Who knows, maybe she somehow got an head injury during the destruction of the Jedi temple, or maybe Kylo used some, so far unseen, force ability on her to erase certain memories from her mind, also once again to safe his own skin. It makes Kylo Rey's savior, which would make it more likely for them to team up during "Star Wars: The Last Jedi" or Episode IX, at some point. But more about this in one of my later articles.

It is obvious Snoke has been using Kylo Ren (or Ben Solo) right from the start as a mere pawn. A pawn to his bidding and one to make the Skywalker family suffer a severe blow, making them weaker, since it is unlikely that at this point Snoke is strong enough to take on Luke. It probably also is true that both Snoke and Kylo at first assumed that Luke didn't survive the purge. It is one of the reason why Luke eventually went into hiding. Not just out of sadness and because he knew he failed with Ben Solo, but also as a fugitive from both Kylo Ren and Snoke, who he knew he couldn't destroy, since Snoke has always been hiding deep into space. The failure of killing Luke and taking the young Padawan Rey to Snoke causes Snoke to not completely trust Kylo and his abilities yet, making it part of the reason why he hasn't fully trained Kylo yet in the dark side of the force. Another reason simply could be that Snoke wants to prevent Kylo from becoming too strong and powerful with the force, knowing that there is still some good left in him and he one day could turn against him, much like his grandfather Darth Vader/Anakin eventually turned against Palpatine.
After all, you also have to remember that Star Wars is all about repeating themes. Rey being tempted to the dark side and Kylo Ren redeeming himself would all fit perfectly into this new trilogy of Star Wars movies. It would explain Rey's heritage and her- and Kylo's further purpose in the saga, as well as Snoke's greater scheme. But again, it is all just my take on things...