I also agree that Kylo was lying to Rey when he said her parents were nobodies. It doesn't add up, and the way he played it it looked like he was lying. My main hope is that Rian Johnson wasn't just drawing the head of a body that JJ Abrams started, that there's cohesion to the story to be revealed in ep 9. I have a theory about what Kylo was getting at when he dreamed of smashing the New Order and the resistance, and starting a co-thrown with Rey, although it's a bit of a stretch and it requires going way back in time. Consider that Yoda was looking for the person who was prophesied to restore balance to the Force. He saw in Anakin that potential person. Anakin goes dark, and Luke is now the hope to restore balance. However, it's actually Vader (Anakin) who kills the Emperor, so he was the chosen one after all, right? Maybe. Fast forward to The Last Jedi. Luke's training of Rey focuses completely on balance: day/night, life/death, light side/dark side, etc. And Rey sees and almost embraces the dark side, even though we don't get the feeling she wants to be evil. Perhaps the message is that the Jedi, by only focusing on the light side of the Force, aren't actually encouraging balance. The light invites the dark, so that as long as their are Jedi, there will always be Sith, and vice versa. So here's where Kylo comes back. He recognizes this problem with the Jedi/Sith duality, and seeks to move past it. He isn't totally evil like Darth Sidious and his ilk, and obviously isn't all good like Yoda's trainees. He may be more dark than light, and Rey is more light than dark, but they're both a mix. He thinks that together, they can actually bring true balance back to the Force, and rule as benevolent despots. This theory is a stretch, but it sort of explains why the peace that the rebellion secured in Return of the Jedi was so short lived (because it couldn't have been more than like 10-15 years based on how built up the New Order is by now, 30 years on). The Jedi were ascendant again, so of course the Sith were going to rise up; the Force almost guarantees this. Both must be killed to kill either. Perhaps Yoda's prophesy has yet to be fulfilled, and Kylo and Rey are the 'true' restorer's of balance. (I put 'true' in quotes, because obviously Disney is never going to let the saga be finished.) I have a lot of other thoughts, but that's the only partially original one.
This is one of the cases in the movie where it had a good idea, but lacked the courage to actually go through with it. Kylo started to get into this...then retreated back to the usual mustache-twirling evil villains that have been the movies' bread and butter.So here's where Kylo comes back. He recognizes this problem with the Jedi/Sith duality, and seeks to move past it.
That's sort of an existential problem for Star Wars though. In the end, Star Wars is supposed to be fun more than anything. It's not a philosophical journey by nature, even though us fanboys elevate it to that sometimes. Trying to play with good and evil instead of just accepting them was a bridge too far for Disney, probably. One thing that hasn't been mentioned here that was a wild departure from Star Wars tradition was the nature of the Force. Apparently, the Force is whatever you want it to be now. I'm actually ok with that. Palpatine alluded to a great Sith lord that conquered death once upon a time (who I think lots of people thought may have been Snoke), so obviously there's more to the Force than we've actually been shown in the movies until now. I think Rian Johnson recognized that and decided to have fun with it. On the other hand it took Luke tons of practice to just pick up a goddam light sabre and Rey was able to Jedi mind trick someone after someone just mentioning the concept of the Force to her in TFA. Doesn't seem too consistent :(