Warning: contains spoilers for Timeless #1!
Marvel's Kang the Conqueror may be a villain, but he's about to fix Spider-Man's most reviled story in decades, all thanks to his villainous nature. Spider-Man: One More Day is ridiculed and lambasted by Marvel fans for breaking up Peter Parker and Mary Jane Watson's marriage in such a haphazard and illogical manner that even Stan Lee disliked the story (he maintained the marriage in the daily comic strip within newspapers). But in clue in Timeless #1 suggests that Peter's marriage is not entirely unsalvageable - at least, not without some time-manipulation on the part of the Marvel Universe's greatest time traveler.
In One More Day, Aunt May is in critical condition after being shot by a sniper who was targeting Peter. As Spider-Man, Peter asks for help from his many friends in the superhero world (but in one of the story's many mistakes, not one of the many super-geniuses in the Marvel Universe can save Aunt May's trivial (at least for them) wound. The demon Mephisto appears and offers Spider-Man a deal: his aunt's complete recovery in exchange for his marriage to Mary Jane. The two agree, but before the deal goes into effect, the cruel Mephisto shows Peter a vision of his future daughter - that, thanks to the deal, will now never exist.
In Timeless #1, Kang visits his extradimensional fortress while investigating a 'timequake' that announces the presence of a rogue timeline trying to reattach itself to the main timeline. Readers see that Kang has easy access to multiple timelines at all times...and one of them depicts a red-haired unknown in a Spider-Man suit. This vision has only been seen once before in comics: at the end of Amazing Spider-Man #74, in which Mephisto reveals that Spider-Man's daughter is destined to defeat the demon when he's already conquered the world. Thus, he made absolutely certain she would never be born.
Kang habitually breaks time travel etiquette and routinely interferes with other timelines on a regular basis - especially if anything or anyone in those timelines pose a threat to him. Timeless has already visited multiple timelines, so it's entirely possible that Kang could visit the timeline in which Spider-Man's daughter exists, take her from her home and bring her to the main 616 timeline. This would allow Marvel to have their cake and eat it too; they can keep Spider-Man young and single (and relatable) while also adding his daughter as a major character)
If Kang decides to bring Spider-Man's daughter into the main universe, the result could even bring back Peter's memories of his marriage with Mary Jane. This would effectively undo the deal with Mephisto, however; and vengeful demon could even kill Aunt May simply out of spite. Regardless, the stars are aligned for Kang to under Spider-Man's greatest mistake.