I really hope this isn't true. I liked TDKR and its ending and I do think JGL has the charisma to lead a Batman movie. But really, I don't think it was intended to carry on John Blake's story - it was just a way of wrapping up Bruce Wayne's story while letting us know that The Batman would continue.
I also think that if they were to make a subsequent movie with Blake as Batman, it should continue in Nolan's relatively grounded universe - a move into a world with superpowers and aliens would be a very dramatic shift. Also, as Captain Craig
says, I want a Superman/Batman link-up to be between Clark and Bruce, not Clark and someone else.
The JLA movie seems like a perfect opportunity to relaunch Batman in a different continuity than Nolan's. And despite Nolan's connection to MOS, I'm very sceptical of the claim that Blake will cameo in that movie - it seems at odds with Nolan's insistence that he wasn't working towards Supes and Bats sharing an onscreen universe.