Dark Horse
If there was one thing Uchiha Mikoto hated it was the way she was forced to treat her deceased friends son. Yes she knew it was for the good of the village and the child, but oh how she loathed being denied the right of honorary aunt.
She hated watching as Naruto was forced to live a life of isolation and despair, but there was no way for him to be integrated into a family without raising suspicion. The Uzumaki were scattered and the Namikaze were gone, Minato had been the last and the only clan with hair that came even close to Naruto's were the Yamanaka's, but even then it would be painfully obvious he wasn't one of them.
Mikoto couldn't have taken Naruto, not without it being the worst kept secret where he came from, a child identical to the Fourth Hokage adopted into the family of his wife's closest friend? Why not just write 'Uzumaki Jinchuuriki of Nine Tailed Fox, Son of Fourth Hokage' on his forehead? The same went for Kakashi and the Third Hokage.
No, it was safest for everyone if Naruto was treated as just another war orphan, let him fade into the background.
Mikoto just hoped that she would see the day he surpassed his parents.
Yes I am well aware that what I wrote is closer to 'Black Sheep' than 'Dark Horse'.