From what i've seen, the evidence for 2b are:
-Nier's 10th anniversary is almost here and absolutely nothing has been announced yet
-Yoko Taro wants nier on switch
-Yoko Taro, in response to 2b being in smash said, "Definitely. Any collaboration, actually. If any of my characters could be in another game, then I’d definitely like to see that. "
-Yoko Taro and Sakurai know each other and have met before.
-No sqaure enix rep in dlc yet
-Sakurai has stated that he played all Drakengard and Nier games and is a fan of Yoko Taro's work. "I’ve beaten NieR:Replicant and NieR:Gestalt. I’ve played every game in the Drakengard series as well. "
-People have been saying there isnt a female rep yet, and the only highly requested character that people want right now for dlc that is a female other than 2b that i can think of is Shantae
-its pretty crazy how many games 2b is in other than Nier:automata, this is the list:
(Lord of Vermillion, Servant of Thrones, Gravity Rush/Daze, Star Ocean: anamnesis, SINoALICE, Final Fantasy Brave Exvius, VALKYRIE ANATOMIA ‐THE ORIGIN‐, Monster Hunter Frontier Z, Soul Calibur 6 and a collaboration with Shadowverse was teased too)
This list shows that Sqare Enix is definitely down to pretty much put 2b in any game.
The only thing i can think of that is holding 2b back from being in fighter pass is that Sora and Geno are being requested, and they are both square enix. But we do have some evidence on Sora being cut so i guess the main problem would be Geno.
Another thing people are saying is that 2b is too sexualized, but that can be fixed easy peasy. (also, Bayo is in smash, like c'mon,)
So yea that pretty much all i can remember from the research ive been doing for the past week.
if i missed anything, help me out and add on to this.
Edit: Hero is a Square enix rep, so add that to evidence against 2b.