But you could say the same about literally every other guest. Ezio doesn't play anything like he does in his game and neither does Kratos. Same with Geralt. And as far as Dark Soul guest goes, I doubt it. DS is known for its difficulty, the challenging bosses, and gameplay. You rarely hear anything about the characters or anything regarding the story for that matter. Including a DS character would be a waste imo, with it being a game where you create your own character (thats what CaS is for).
As far as 2B goes, I'd prefer Nier or Kaine as a guest, but I wouldn't be opposed to her inclusion. It would make sense, given her popularity. An as far as her being "too futuristic" sure, but many people demand Asholette, who is
1. A robot just like 2B
2. Is ironically more mechanical than 2B
If you put them side-by-side, 2B looks far more human. If she's in, I'll be fine with it. She'll draw in more people to play SC6, just like Geralt will.