First a bit of background, Rey parallels Luke every chance she gets. This is especially obvious in the Force Awakens, but also appears in the Last Jedi. Kylo on the other hand seems like a parallel of Vader, but that’s actually not quite right. What he really is is an inversion of Luke.
Luke is the heroic son of a villain, he is tempted by the Dark Side, he yearns for a relationship with his father, and he refuses to kill his father.
Kylo is the villainous son of heroes, he feels a call to the light, he rejects his family, and he kills his father.
So keep that in mind. Rey is a parallel of Luke while Kylo is an inversion of Luke.
Now take a look at this…
Please note that even their facial expressions and posture are very similar between these two scenes.
On the other hand Kylo…
… is an inversion of Luke.
Note that it appears that Kylo’s burning ship is also on Ahch-To.
What does this tell us about Kylo’s final destiny. Please consider that perhaps the inversion is a bit deeper.
Luke went into self imposed exile after making a terrible mistake. He ensured that he would remain in exile by using water to render his X-Wing un-flyable. Luke’s exile was a time of great depression for him and a time when he felt deeply burdened by his past.
Now invert that…
Ben Solo goes into self imposed exile after finally making the right decision and coming back to the light. He uses fire to render his TIE fighter un-flyable. Ben’s exile is a time when he is finally at peace and a time when his burdens begin to lift.
It’s possible that Rey isn’t actually on Ahch-To for this particular scene. Rather this is the final Force Skype scene in the film where Rey watches as Ben’s exile begins and the two bid farewell to each other.
Self imposed exile would be an interesting ending for Kylo Ren for several reasons. First and foremost, its not a direct repeat of Vader’s self sacrifice redemption arc in Return of the Jedi. But it also manages to conclude his story in a satisfying way without requiring the son of two beloved characters to die a villain. Secondly, it allows Lucasfilm to keep the very interesting character of Kylo Ren/Ben Solo around should they ever want to tell future stories about him set after The Rise of Skywalker.