Possible events which can happen in 650 chapter:
1) Naruto get Yin Kurama from Minato. Chapter called "Finally Whole again "
2) Sasuke awake Perfect Sussano, or at least uses legged Final Sussano v4.
3) Kakashi comes back
4) Madara's trump card
5) More info about Sage and The God Tree
6) Naruto uses Tailed beasts chakra(unlikely)
7) Naruto meet Sage of six paths(Too early...., more likely around 660 or even 700 )
8) Shinobi Alliance army dies
9) The Five Kages entrust their will to Naruto and die. Rage of Naruto
10) Naruto surprass The Hashirama, so All Hokages are finally surprassed
11) Orochimaru surprise us with doing some stuff
12) Sage's sons appears or their backstory is revealed to us
That all I can think of
Hope you like it