Whether true or not, this should not happen with the solo franchises. If WB wants a JLA movie then create a completely different franchise apart from the solo films. Nolan's Batman does not have to end up in a JLA film, same with the new Superman and Reynold's Green Lantern. JLA can create their own visions of these characters apart rom the visions and stories we see in the solo films.
Marvel wants all their films to eventually blend into The Avengers, and that's fine, but it doesn't necessarily have to be that way. The solo films, to me, can work as a way of strengthening the audience's relationship to each hero so that if a JLA film ever does come around there wont be any catch-up and everyone will fully understand who each hero is. The only real problem with this is audience awareness, and being able to understand the solo films and the JLA films don't exist in the same universe, and some plotlines could become mixed and confused.
Warner Bros. should let all the solo franchises playout in their own way without forcing in a "oh, did you hear about the guy from Gotham?" moment just so they can set up a JLA film. JLA can be approached from other angles.