As excited as we all were to finally see Star Wars: The Force Awakens, the film left us with just as many questions as it did answers. Of all the things we saw, it's possible that nothing was quite as curious as Rey's lightsaber induced vision/flashback. Now, it appears that we may have more of that on the way. In fact, it sounds like there may be plans to show us the same flashback sequence in Star Wars: Episode VIII, but to include more details.
Specifically, it appears that there may be a scene in Star Wars: Episode VIII that shows us more of what happened to Luke Skywalker and his Jedi school that led him to disappear. According to Making Star Wars, the word is that there's a scene in the new film that includes Luke, Kylo Ren, R2-D2, and Rey, along with several adolescent kids who are apparently the dead padawans that Kylo and his Knights of Ren look to have taken down. The fact that an adult Rey is in the scene, but that she doesn't apparently interact with the scene at all, indicates that this is more of her vision, as we saw in Star Wars: The Force Awakens.
The rumor does not indicate exactly how this vision is triggered, or if it does, MSW isn't talking. They do seem to be more vague than usual, which implies they may know much more than they're letting on.
In addition to potentially answering some questions about what happened to Ben Solo that made him Kylo Ren, as well as letting us know more about Luke's time between trilogies, it's also possible that this second vision may actually explain why the first vision happened at all. Flashbacks and visions of the past have not been traditional mechanics of The Force, let alone side effects of picking up old lightsabers. Whatever induces this second vision could help explain why they're happening to Rey in the first place.
The fact that we may see more of the flashback sequence seems to imply that some details in it may be important to the greater story. The purpose of not giving us everything the first time around wasn't simply to keep us confused. They could have explained the flashback in Episode VIII without showing it to us. If they need to show us more, there could very well be something important to the plot that we need to see.
The flashback scene, with dead students lying about, was one of the darker scenes in all of the Star Wars films. If Star Wars: Episode VIII is as dark overall as Star Wars: The Empire Strikes Back, we could be in for one of the blackest scenes ever.