The Old Mixer wrote:
Who says they're trying to set up a new Batman franchise. It's too soon, and they've got plenty on their plate without investing in that.
I'd dare say that if they seriously planned to start a new Batman franchise, introducing their new Batman in a Superman film would be problematic at best...but it works just fine if they only plan to use Batman in team movies for the time being.
At the start of the year, I read that WB were planning to use the JLA movie to introduce their new Batman. If that story did reflect their thinking at that time, it looks to me like they've just readjusted their plan so as to use the Supes/Bats film to do so instead.