Yes, that could work too. I'm not sure that they will do that though - I think Batman is different from their other gallery of heroes in that he is a proven box office draw in not just one but two series of successful (financially anyway) movies. No other comic strip hero has achieved that yet (Spider-man is on his way, admittedly). I still tend to the idea that in this movie Superman is getting a boost from him as much as the other way round, even if this is an as yet-unseen version of Batman. Of course, if the next film follows the Dark Knight route of the sequel being way more successful than the first in the series, then Superman is well placed to springboard Wonder Woman etc onto the big screen. And, as you say, in a totally different fashion to how Marvel have done it.