I'm gonna be honest, I don't think KOS-MOS has much of a chance for FP5. Think about it. All of the fighters so far have appealed to different demographics:
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: Newest generation of gamers, PS4 fans, fans of new JRPGs
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:Oldest generation of gamers, fans of older JRPGs (and older RPGs as a whole)
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: Older (but not oldest) generation of gamers, western fans, without question the most widely demanded newcomer so far
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: Fans of traditional fighting games, SNK fans as a whole, Latin American fans
KOS-MOS doesn't fill any missing demographic segments. Additionally, she's not very widely known. Her individual games haven't been localized, which is a huge issue. I know that Sakurai said that being recognizable is less important than being fun to play, but it's still possible that he takes recognition into account. The biggest thing going for her is Namco's history of throwing her into games, but we don't know if Namco had any authority over thee DLC choices. It was Nintendo that gave Sakurai the list of potential newcomers, not Namco.
I'm not saying that she has a bad chance of being in, I'm saying don't romanticize her chances. Because to be honest, I think another fighter like Lara Croft or Doomslayer has a better chance.
Also, who is "many" who believe she is FP5 because she hasn't been deconfirmed by Verge? I'd like to see that. And haven't you been all over Verge and associated leakers for getting TGA wrong?