rushed perhaps but i still think he had them in mind for other characters kids. Sarada is just way too Karin and Sasuke, and Boruto has multiple Sakura and Naruto elements.
Nah im pretty well convinced he had them in mind as next gen progeny of NS and SK
Boruto was the next Naruto set to inherit Kurama when he was ready the marks would have come then
Sarada for me was Sasuke and Karins Kid and shared some fo their abilities karins uzumaki blood which would lead to better control of her Sharingan but more so I think she was meant to idolize Sakura hence some of Sakuras outfit choices which leads to her becoming the powerhouse she would become.
It was proven in the manga Sarada is Karin's daughter and not Sakura but Kishi backpedaled remembering he needed to keep with the SS canon crap.