I know officially his name is Sai Yamanaka (which could be a lie), but what I'm asking is: could he have Uchiha DNA?
Sai was kept underground for the majority of his upbringing and hidden, furthermore within the foundation he mastered the suppression of all emotion, and Tobirama Senju explained the the Sharingan is awakened with extreme emotion.
Itachi only had so much time to slaughter the entire bloodline; any Uchiha out on missions may have survived, hidden within the Anbu. And when you are born a Uchiha, you can deactivate the eye. Maybe it's possible there were still Uchiha within the village as part of a 'witness protection' service to keep them hidden. (It's possible that it was being planned for some time and the Anbu Uchiha were pulled out of service, but it's still possible they didn't.)
If both those statements are true, doesn't that mean Sai could be an Uchiha? I haven't started Boruto, if this was explored there I don't know, but Sai feels like a side character and I doubt it.