Naruto is an Uzumaki. He's a reminder Kaguya's past. His use of sage mode is akin to her abilities with the Byakugan, as well.
Sasuke is just part of Hagoromo's meddling. The only thing that makes him remotely relevant at this point is the fact that Orochimaru used the enzyme Juugo's clan uses to harvest nature energy - which makes him a distant echo of Hamura.
I am sure the role of the Uzumaki will be explained before too much longer, as it was the Uzumaki and the Hyuuga who sealed Kaguya into the Holy Tree (before her will spawned the Juubi). Likely, it was Kaguya's lover who actually performed that sealing.
Of course, it wouldn't have to be done if Hagoromo hadn't arrogantly sealed away her compassion because he's the "enlightened sage of six paths" who "understands human suffering."
Of course, after he did that - she turned into a sociopath bent on domination and control. Which is why the Uzumaki and Hyuuga had to seal her in the first place (hence the Eight Trigrams seal used by the Uzumaki and remains as the mark following the use of the Dead Demon Consuming Seal).
Although that plan wasn't foolproof, either - as Kaguya's will spawned the Juubi before Hagoromo and Hamura sealed it (which was when Hagoromo - not Kaguya - created Black Zetsu... because he's 'helping' - or so he believes; though it must be remembered that his methods are subversive and rather inconsiderate of the lives of those involved - evidenced by the seal he created that Madara later used to control Obito and Rin - likely a similar seal to the one he used to seal away Kaguya's compassion - or try).
So, there's a reason why she's rather fixated on Naruto.
She has the Byakugan.
She can see it.
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Just as Neji did.
In the end - Naruto and Hinata share the same destiny. Just as Kaguya and her Uzumaki accomplice set the stage for the following millennia; so, too, will it be Naruto's.
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Before much longer - I suspect we will get some of Kaguya's telling of events. I also suspect we will see her compassion freed from the clutches of Infinite Tsukuyomi (though whether she accomplishes this on her own, or not, will be interesting). At which point things will get very interesting when Kaguya confronts another Byakugan. Someone will have to mention the white elephant (eye) in the room.