699 wouldn’t have been a terrible place to end it, but I have to say that “but did Naruto become Hokage???” would have always been an unsatisfying note in that case.
It’s just that “He DOES become Hokage! Except he misses his own inauguration and is overworked and miserable and out of touch with his kids and his best friend is never around and he sleeps on the couch and orphan children are still being abused and experimented on under his watch 😀 😀 :D” is objectively a worse ending than that.
I think an open-ended hopeful ending would be Naruto as a relatively young Rokudaime–18-20, let’s say, which isn’t ridiculous when you consider that Gaara is Kazekage before he’s 16–being inaugurated.