Probably to pronounce NS dead and the canonization of NH and SS.
Joke aside , there is no escaping it all roads from chapter 3 to the present lead to NS if things were ambiguous before the war outbreak and chapter 615 , well there is nothing ambiguous now. Its a cohesiveness of all the pieces of the puzzle the last piece is her realization.. 631 was a big chapter for some for other a huge downfall ..
I agree. NaruSaku is inevitable now, especially after 631. There's no going back now, Kishi! Prepare the canon!!