Nightwing is for sure going to be playable in this if the rumours of the Batfamily focus are to be believed imo. Cass lol no :/ I guess it'll be Barbara and Tim for certain on top of Nightwing.
I also hope WB doesn't pull some shit like that (I think they had some bullshit in the Mordor sequel, but I'm not sure). Although I'm at the very least expecting co-op and the like (which could be fun, say, if it's couch co-op, but I don't want a GaaS focus on multiplayer even if they still give you that option).