WARNING: The following contains spoilers for Chapter #61 of Boruto: Naruto Next Generations, “Madness,” by Masashi Kishimoto, Mikio Ikemoto, Mari Morimoto and Snir Aharon, now available in English from Viz Media.
In the Boruto manga, fans have been left trying to guess what's up with the dark future seen at the beginning of the story for some time now. That time-jump showed an older Boruto battling Kawaki, who seemed to have destroyed Konoha and killed Naruto. However, with the teens as brothers in the past under Naruto's care, it's uncertain what would have sent Kawaki over the edge, especially as he's currently keen to protect the Hokage. Well, in Boruto #61, the boys' evolving bond may explain this heel turn thanks to a telepathic link.
It's revealed when Kawaki wants to escape Naruto's home to either find weapons to fight Code or some means of powering himself up. He leaves a shadow clone in the house with his chakra signature, while escaping Konoha by nulling his own. The shocking thing is, Boruto can still mentally communicate with him, although they don't know how it's happening.
Kawaki is annoyed, believing the way Isshiki prepped him as an Ōtsutsuki vessel -- and how Momoshiki has been possessing Boruto -- perhaps allows this connection. However, that intrinsic bond could provide a gateway for Momoshiki to possess Kawaki. If Boruto can lock into Kawaki's mind and Momoshiki can take over Boruto's, there's a chance for Momoshiki to jump into Kawaki.
He could manipulate Kawaki's Karma mark that failed with Isshiki, overwriting it with his DNA. Kawaki's a more fitting vessel than Boruto so Momoshiki would actually be stepping up, succeeding where Isshiki failed. If that's the case, the Kawaki in the future might be Momoshiki -- and Boruto just doesn't know.
Boruto is still fluid as to the rules of Karma at the moment -- with Code having a different one allowing him to harness Isshiki's powers without being possessed -- so there's plenty of room for new developments. Even if Momoshiki doesn't fully possess Kawaki, the teen might figure out how to sap his powers and could become corrupted along the way -- akin to Sasuke from the Naruto era. It'd bring the Boruto and Kawaki rivalry full circle because instead of seeking power and being corrupted to destroy Konoha like Sasuke, Kawaki might run afoul of his new family by wanting power to save the Hidden Leaf village and its people.
It would place an intriguing remix on the Boruto franchise. With Momoshiki knowing Kawaki's movements and being in his mind -- plus having control over Boruto's body -- setting Kawaki up as the backup would also continue the villains' themes from Naruto. Madara used Obito, but Kaguya was pulling their strings in the background, so Momoshiki would once more get to prove his alien species always have contingency plans as puppet masters in the background.
Adding weight to this theory is the idea that if Momoshiki plans to take Kawaki, he could still possess Boruto and feed that body to the God Tree. It'd allow Momoshiki to be reborn in Kawaki after the sacrifice and feed on the chakra fruit, achieving the godlike status and overall evolution their species were always meant to partake in roving from planet to planet.