I could go either way on revealing Batman ahead of time. Of course I could see them trying to keep it under lock and key, but at the same time… the show being confined to Gotham (and specifically following so closely behind the end of the film), I don’t think they can get away with Batman NOT being a factor in this. Even if he’s not the main character or commanding equal time with Penguin, it seems almost certain to me that he’ll be in the mix. So I don’t think it hurts to light up the signal to let some audience members know about it.
And then, in that case, SDCC is definitely the way to go.