Although the Boy Wonder doesn't make an appearance in Rocksteady's Arkham games
Yes he does! He makes a brief appearance on the rooftops when you're chasing that ninja girl in Arkham City. There's also the Harley Quinn DLC.
I would love some Batman/Robin free-roam in Gotham co-op though.
As for what I've seen of Batman's suit for this game, I'm not really liking the look of it. It looks a little too armoured and "tech-like" for my tastes.