Having read through the achievement list, I can speculate on the following:
All of Scarecrow's inner circle, or top lieutenants will be Most Wanted side quest material that the player has to apprehend, similar to Poison Ivy in the Going to War footage that was recently released.
So I wonder what characters will fill in the role of traditional boss encounters. Asylum had Bane, Joker, Poison Ivy, and an assortment of Titan enhanced thugs. City had Solomon Grundy, Ra's al Ghul, Mr. Freeze, and Clayface. I have to assume that the Arkham Knight will be one of them, but who else could Rocksteady use? Maybe Killer Croc, who was never really given a traditional encounter in Asylum. An aerial battle with Man-Bat sounds intriguing, although nothing is confirmed, but him and the Ventriloquist are the last characters who haven't been adapted into the Arkhamverse from the classic Animated Series era when you think about it.
As much as I love the Rocksteady series, it seems like they've never really put heavy priority into developing their boss encounters. it's almost like a lost art. Something that the Japanese still trumps western developers.
