Just thinking about this today....
I think the decision to go NH came just before the beginning of the war arc. Because up until then, when Naruto was seeing everyone on the battlefield and he saw Sakura alone, everything was still moving along believeably.
But that was the last truly NS moment. From then on, every Sakura panel got equal Hinata time. And Hinata got more lines, and her interactions became more and more overtly romantic.
The decision may have been made sometime before the war arc, but wasn't put into place until after the start of the war. Hinata before then is simply nonexistent in the storyline.
After the Kage Summit arc, everything got really disjointed and scattered. That's when elements of the story stopped making sense, characters were introduced, backstories were explored then resolved, all just to bloat the plot and drag it on. I think the decision was made as to how to end it, and then Kishi just went on autopilot till it was over.