Ok, so I'll be the first to admit that this theory is a little bit out there, but now that we have another 7 months added to the wait until Episode 8, we might as well have a little more speculative fun.
What started me down this path was half-jokingly asking myself "How bad of a Jedi is Luke?" If we're to believe everything in the films so far at face value, Luke essentially blows the one job he had after Return of the Jedi and fails so miserably that he exiles himself to prevent ruining the galaxy any further with his ineptitude. Not only is he inept, he must also be incredibly weak. Allow me to explain:
Between the film and the novelization we know that Kylo Ren is roughly 30 years old in The Force Awakens, and that Han had not seen his son as an adult. Let's just assume 18 is the age of adulthood in the Star Wars Universe, that means the oldest he could be when he slaughters Luke's new students is 17 (roughly Luke's age around the time of A New Hope). Despite his penchant for Jedi antiquing as demonstrated in the new extended canon, I can't imagine Luke is not present when his students are murdered.
So if we take it at face value Luke is unable to overpower a freshly turned to the Darkside Ben Solo, who later in life will see himself bested--though wounded at the time--by a completely untrained Force Sensitive named Rey. Even if it's a matter of he was unable to slay his own nephew, that would seem uncharacteristically weak for a now more seasoned Jedi Master Luke Skywalker. After all, he has witnessed first hand the power of the Darkside and what happens when it goes unchecked. At best it seems irresponsible if not outright negligent for Luke to abandon the galaxy and hope someone else steps up to handle Kylo.
Now in the film it's not explicitly mentioned that Kylo carries this out with the Knights of Ren, though it's implied via the Force Back vision Rey has. Even if he does employ the help of his 6 other buddies, they clearly are not carrying lightsabers in the vision. Are we to believe that the field of dead bodies we see in the vision is carried out by a 17 year old, his 6 friends, and the other Jedi in training, some who theoretically could have been under Luke's tutelage longer, were unable to stop them?
This doesn't seem very likely, even if we were to argue that just because Han hadn't seen Kylo as an adult, that he didn't come to wherever Luke's academy was as an adult to wreak havoc, but that doesn't seem likely as clearly Luke seems to have been missing for a very long time by the time The Force Awakens kicks off.
So now to the purpose of the post. I'm convinced there's more to Luke's exile than just self-pity, and with John Boyega hinting that Episode VIII is going to be 'very dark' especially when compared to The Force Awakens, I'm pretty sure it's a deeper turmoil. I think we are being set up for another 'from a certain point of view' moment, since The Force Awakens goes out of its way to hit us on the nose that Kylo killed all the new Jedi in training.
My theory is that when Ben turned to the Darkside and peeled off other apprentices to start his side project known as the Knights of Ren, Luke Skywalker realized he had a bigger problem on his hands than a miscreant teen with an identity crisis who had run off with some of his students. If he was unable to prevent his own nephew from turning, he realized there was a critical flaw in how he was training the next generation.
Rather than unleash a potential of darksiders on the galaxy Luke takes a drastic measure, and eradicates his own students as a preventative measure. As we saw in Shattered Empire when he wipes out the Imperials using the Force to throw thermal detonators back at them, the post-ROTJ Luke is not immune to dealing death for what he sees to be the greater good. This is not the Luke from the end of ROTJ who is willing to look past the evil on the surface to search for the good still dwelling within.
What he's not willing to do though is kill children. So he takes his youngest apprentice, builds a Force wall in her mind and dumps her on Jakku (whether or not she's his daughter I'll leave up to other's to guess). His self-imposed exile isn't a prolonged pity-party, but instead an effort to figure out where he went wrong. That's why he's gone in search of the first Jedi Temple, in the hopes he can do what the first person to become a Jedi must have done -- build a functioning order.
In the leaked script Luke's demeanor is described as 'tortured'. Is this because he's staring into the eyes of his daughter and is having feels about having abandoned her knowing that her cousin was a Sith-wannabe with a deep hatred of all things named Luke Skywalker? or is it because she reminds him of his ultimate failing in rebuilding the Jedi, and the sacrifice he had to make in order to carry out his destiny? Does he see in that moment a shot a redemption and all the burden that will come with it?
Luke running away to hide isn't characteristic of the man that Yoda instructed to carry on the legacy of the Jedi. You may argue that neither does slaughtering potentially innocent future Jedi -- unless post-ROTJ Luke realizes that being the Last of the Jedi isn't easy and is not approaching it with a farm boys naivete. That would make it difficult but believable that Luke sees his flawed students pose a bigger threat to the galaxy than he's unwilling to risk and does what seems to be unthinkable.
Luke, in the new canon, shows a penchant for finding things of the old Jedi to inform how he's going to shape the new Jedi. I believe his exile is an effort to find what he can to not only stop Snoke and Kylo Ren, but finally fulfill his mission to rebuild the order. Remember if we assume he goes into exile shortly after Ben turns and the Jedi are killed, neither Kylo nor Snoke's threat is mature enough to merit Luke hiding out for his own safety ala Obi-Wan and Yoda.
Now I know what you're thinking from a few paragraphs ago. In Rey's vision we see Kylo's lightsaber tear through a padawan. Or do we? In both the movie and the novel it's implied Kylo knows just who Rey is. I believe the scene we see in her vision is not of the Jedi slaughter at all, but related to their crossing paths in the past.
I know this seems like an out there theory, but it would certainly take the lore in an interesting new direction. So much of the Original Trilogy was very black and white, but what would make Luke more interesting as a character now, is if he's had to question some of the very beliefs he thought defined him as a man and as a Jedi. If he had to do something he thought was 'Dark' in order to protect the 'Light'. If the 30 years truly tested his resolve. Either way Episode 8 will hopefully shed some light on all this speculation, but in the meantime, let's discuss!