Boruto has the opportunity to properly explain a lingering plot hole from the end of the original Naruto series. The final arc of Naruto's story is centered the Fifth Great Ninja War, as the various villages unite to take down the combined forces of Madara Uchiha, Obito Uchiha and Kabuto. While Madara initially intends to fight using his Zetsu army, Kabuto bolsters the evil ranks considerably by using the Edo Tensei reanimation jutsu, which essentially brings back every dead character in the franchise. Among the revived are Itachi Uchiha, Zabuza and Haku from the very first arc, and an array of past Kage. This allows one final farewell or big moment for some of Naruto's most popular characters, but conspicuous by his absence was Jiraiya.
Jiraiya is the only major Naruto character not to be revived in the final arc, but the anime and manga opt for different excuses as to why. In Masashi Kishimoto's original story, Kabuto claims that he could get a big enough sample of Jiraiya's DNA to reanimate him, but Obito (still masked at this point) says not to push his luck. In the anime, Kabuto simply says that he can't reanimate Jiraiya because his body is at the bottom of the sea. Considering all the other powerful ninja Kabuto brings back, this is a weak excuse, especially since ninja were renowned for properly disposing of comrades' bodies after death. The real reason Jiraiya isn't reanimated is to protect the integrity of the character's emotional final scenes, but in the context of the narrative, his omission in the final war is certainly odd.
Now, however, the Boruto sequel series has an opportunity to finally account for Jiraiya's absence in Naruto's final arc. The main villains of Boruto are a shady group called Kara, who are secretly led by a member of the Otsutsuki clan. Among Kara's powerful ninja roster is a white-haired man called Kashin Koji, and fans have drawn many parallels between this character and Jiraiya. Some speculate that Koji could be Jiraiya's son, while others claim that Koji and Jiraiya are somehow one and the same. It's also possible that Kashin Koji is a clone of Jiraiya, since Kara are heavily involved in genetic manipulation and the concept of clones has already been introduced in Boruto via the Shin character.
Whoever Kashin Koji eventually turns out to be, the reveal could potentially help explain why Kabuto didn't resurrect Jiraiya. If Koji is a clone of Jiraiya (or an artificially-created son in the style of Mitsuki and Orochimaru), this would suggest that Kara had already collected up the Toad Sage's DNA for their own use, leaving Kabuto with nothing to work with. Kara have been operating in secret for years, and artificially creating fighters appears to be their chief recruitment method. Obviously, if Kashin Koji is Jiraiya this would also retroactively account for why Kabuto couldn't resurrect him - one has to be dead before they can be reanimated, after all. Finally, even if Kashin Koji is confirmed to be Jiraiya's natural child kept secret all these years, the character in his youth might've already rounded up his father's DNA, perhaps to prevent Kara using it against him.
Any of the above solutions would unavoidably feel like a Naruto retcon, retroactively changing the reason why Jiraiya wasn't subjected to the Edo Tensei, but they would also be more sturdy excuses than not being able to find Jiraiya's corpse, or as in the manga, just not being bothered. This kind of hole-patching is one of the biggest advantages to making a sequel series in the first place, and although Boruto fans are already eager to learn the truth about Kashin Koji, the reveal would be even sweeter if it helped clear up an old inconsistency from the Naruto days.