This might sound repetitive but I found these panels interesting
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I am 100% sure this new guy is not a survivor because even if Itachi missed someone, Obito and Danzo also wanted to kill all of the clan and both of them have sensors to find out anyone they want.
So he is an experiment like Yamato
Yup, it's foreshadowing. I think dude is from another branch of the Uchiha from years ago. Maybe a small fraction disagreed with the aliance with the Senju and roamed the land, breeding with other clans, resulting in light colored hair. I think maybe over the years, Orochimaru discovered this small side branch of the Uchiha and that's how he'll help shed some light on what's going on.
That said. This whole story is leading up to Sarada learning the history of her cursed clan and the trauma from that news will cause her to awaken the sharingan.
I think the real red herring with this whole story so far is that this is all about who her mother is and not about hiding the past from her. The secrets everyone is keeping from her isn't based on maternity, but on hiding the shame of her father's history.
If they have to explain who Karen is, they have to explain how she met her father, why he left the village, etc.
It would be devastating to her.
I also theorize that she'll want to become hokage to change things and that will be the root of her rivalry with Bolt.