WARNING: The following contains spoilers for Boruto: Naruto Next Generations Episode 181, "The Vessel," now streaming on Crunchyroll, as well as for manga chapters not yet adapted to the anime.
In Naruto, redemption has always been a major theme. No matter how sadistic the villain -- well, apart from Madara Uchiha -- there's always room to come back to the light. It's something Naruto often asked of his enemies, realizing a united shinobi world would be better for everyone.
The likes of Nagato, Orochimaru, Itachi and Obito all did this, and now the Boruto series could be prepping another villain to be redeemed. This is none other than Naruto's deadliest enemy, the Rabbit Princess, Kaguya Ōtsutsuki.
Naruto and Sasuke had a legendary fight against her in their teens before eventually sealing her away. They couldn't kill her and, knowing it'd be too dangerous to risk trying, they went with the easier option. It's an unbreakable seal, though, harnessing the power of the Sage of the Six Paths, so they don't have to worry about anyone else being able to crack it and free her from her prison.
But with more alien threats coming from other Ōtsutsuki clan members, Kaguya will be needed. Naruto, as Hokage, struggled to defeat Isshiki and after seeing the likes of Momoshiki, Kinshiki and Urashiki invade, it's clear the Ōtsutsuki won't stop coming to steal whatever the Earth has that they want. The difference is Kaguya wanted to protect the planet, ergo why she shared chakra with humans as she fell in love and even had kids. The others, though, simply believe in feeding humans to the God Tree and Ten Tails Beast, which is more twisted than Kaguya just wanting to leave them in a dream state so there could be peace.
However, that love of the planet doesn't excuse her actions. Kaguya brutally punished mankind after giving up on them and her sons, Hagoromo and Hamura, tried to talk her out of it but failed, which happened again when their descendants, Naruto and Sasuke, battled her. But time heals all wounds and Kaguya could return now that the world's united and is that better place she always imagined. She called Naruto naïve years ago, but nations have come together at last, working to help each other grow and improve, which was always her dream.
If they need help, Kaguya's the ideal person to ask and with Naruto and Sasuke's power, plus the Karma mark allowing an Ōtsutsuki to be reborn, there are ways to explore bringing her back. She's not a fan of her clan so they can use this, plus her love of the planet to help her atone. Kaguya has been a tragic villain as she couldn't stand the hateful ways of humanity but, with Boruto's generation fighting as well, there's enough to get her to believe in people again.