Why would it need more than 75??
NS:Generations only had just over 70. & that included the whole "before time-skip" generation.
They wont be in it this time round, so thats like 15-20 more spots that they need to fill, to get the same number of Characters.
The only new characters we've seen so far are hanzo, mifune, Gin, Kin, Dariu & possible 7 swordsmen?
(i'm not including sasori, asuma, etc... Because its likely that a lot of them will just replace the old versions, so will not take up an extra space)
So so far we have only seen an 5 extra (possible 12) characters. So they still have a lot more spaces to fill.
My guess is Edo Kage (another 4 spots), Edo Nagato & itachi (another 2), Kakazu, Dan, new Tobi & the Edo Jinchuriki (another 7)
Even with all those names, you are still left with another 10 spots left to fill??
(i know they were filler, but i am hoping they add the scorch-style & explosion-style users. Would be cool.)