The greatest testament to this horrendous ending is the movie, naruto the last. I think it decided the ending that we have today. I'm not saying that NS was always a red herring, NS has 10+ years of development and in my opinion this pairing doesn't even need a kushina parallel or some life/death situation, it can stand on its own. Naruto and sakura could've come together if they just took that one last step of accepting each other as they are. They don't need some dramatic moment or an entire friggin movie!
With that said, I don't believe a word of what Kishimoto says in his interviews. Its been proven time and again that he changes his story in every new interview. I advise all of you not to believe anything he says but instead look at the manga. Because the manga shows every single creative decision he has made regarding the characters and story.
Now as to why I think NS became a red herring in the last years of the series. I came across this article last night.
Its a 2012 article about a new naruto movie being announced for 2014. Now this movie is the last, meaning by this point in 2012, people at studio pierrot had already started working on the production of this thing. It is safe to say that the ending was decided in 2012 because it was Kishimoto who provided the early designs for all the characters. the chapters containing the CPR scene and the kushina parallel came out in 2013 so yeah, I do think Kishimoto is despicable enough to lead his readers on by manipulating the wishes of the main characters dead mother.
I have worked on a few movies where I'm from and let me tell you that it takes at least two years to produce an animated movie. Writing the script, coming up with designs, drawing the storyboard, doing the actual animation and then compositing the entire thing takes a lot of time. So my guess is that this ending was decided in the last 2-3 years of narutos run.