Diggle is afaik the only CW character who had some staying power in the comics.
When it comes to Ryan I guess after the Batgirl issue we might have better idea if that was just a cameo, or if they want to build that character up for something.
But I don't know how they should make her becoming Batwoman in the comics work, unless they take the time to establish some connection between her Kate, otherwise it would seem to me more natural if Barbara would transition to Batwoman and Steph and/or Cass would take over as Batgirl(s), should Kate retire for some reason.
And with Bette Kane, Rene Montoya and Helena Bertinelli there are at least three other characters that would imo at the moment work better as replacements than some newly introduced character.