Another theory I've sen floating around?

I alluded to this but there's a distinct possibility that Boruto nd Himwari have Kaguya's chakra.

Kaguya's power seems to have been divided among Hogaromo and Hamura. and then was literally divided into the Nine Tailed Beasts.

Naruto has Hagaromo's chakra and that of all nine-tailed beasts, which explcitly grants him the chakra of the Ten-Tails. Hinata has Hamura's chakra.

We know that it's possible to pass chakra down from parent to child...

So while they do' have the ingredients to recreate Kaguya's biology or serve as a vessel for her, it's entirely possible that all the ingredients needed to recreate Kaguya's chakra would have been inherited by Bort and Himawari.

...but there's more. The manga depiction of the Jogan, as shown in the Boruto manga's flash forward in the first chapter, doesn't look that visually distinct from an unactivated Byakugan. It was the anime that made it blue with a black sclera.

The image we see of the "Otsutsuki God" shows them with three identical eyes and a wall of eyes behind them and in the anime they look suspiciously similar to jogan, then when we see the body of Shibai who is just outright said to have become an Otsutsuki God he looks an awful lot like the one that Ishiki was talking about except his eyes... One Senrigan, one Rinnegan, and one pale eye without a pupil that I thought everyone assumed was a Byakugan but may well in fact have been a Jogan... in his right eye, the same eye were Bort has his own Jogan.

Regardless of where Kaguya got her ten-tails from, Shibai probably lived and "died" on the Earth since his body is here, so his data was probably in her chakra fruit—the fact that his Rinnegan is in the same location as her Rinne Sharingan and the fact that she went from one of the weakest members of the clan to one of the strongest after eating Earth'schkrafruit supports this.

So it may be fair to assume that Kaguya possessed Shibai's various abilities and just never awakened them...

And stepping onto the novels for a moment, according to one of Sakurra's focus novels, Naruto's DNA has codes in it that, reverse-engineered, can be used to synthesize Kurama's chakra. Given that prenatal exposure to Kurama's chakra is responsible for Naruto's whisker marks(which we inherited by both of his children) i seems plausible that prenatal exposure to chakra causes mutations that make you more similar to who inherited it.

Or, in other words, by inheriting the ingredients for Kaguya's chakra, it is entirely possible that Bort and Himwari are more similar to Kaguya than they would otherwise be... And that, in Bort's case, due to gene recombination and stuff, this resulted in the awakening of latent traits Kaguya got from Shibai's data.

Supporting arguments for this are Boruto's horn when he goes Full Otsutsuki. When Kawaki or Jigen go full Osutski, drawing on the full power of their Kama marks, they grow Ishiki's horn.

...Bort doesn't grow Momoshiki's horn thought. the shape is vaugly similar but it's coming out of the wrong place.

the horn that Boruto grows... Looks like a mid point between Momoshiki's and Shibai's.

The person I got this theory from goes on to speculate that Himawari will awaken the Tenseigan due to having the eyes of a Hyuga and the chakra of an OTsutsuki but... I don't think I like that theory.

Especially in regard to her post-time skip design. Particularly how long her hair is.

All the way back in OG Naruto part 1... Sakura having her hair be really long was treated as a sign of immaturity. She didn't have a practical reason for it, it was a liability. Her cutting her hair after it got grabbed and, by extention, keeping it shorter from then on out was presented as a sign that she was taking being a ninja more seriously.

And that is consistent—the only people we see with super long hair either have a practical reason for it, like some technique using their hair—even ino has that thing where she uts her hair and scatters it around to have more versatility—or isn't really a frontline fighter and even then, most such characters have it tied back.

So either Himawari. who is now training to become a ninja and has a serious drive to get stronger has a practical reason for her hair to be that long... Or she's going to get a practical reason. Himawari already shows a disturbingly lethal affinity for the use of the Byakugan in combat.

Not to suggest that Hima is going to get all of Kaguya's powers but manifesting her unique Byakugan ability and related Kekei Mora is plausible.