Yes. This is exactly what I mean, Didio went to Morrison and pitched a GL book starring Hal Jordan, and they accepted, Didio also went to Morrison and pitched a Superman and The Authority book and they accepted it too. Morrison was sold on the idea of writing the books, but did in the way they wanted to do it, The Green Lantern started as a policial procedural in space and became a examination of Hal's character history and DC comics as a whole. Superman and The Authority was supposed to be Clark starting to go more authoritarian and end up as something different.
In both cases the initial idea already existed, and would possibly happen anyway, we know S&TA would, Morrison only took the job and put their very particular spin on it. Its what I believe happened with Waid, editorial more than likely offered him a comic they would do anyway, he accepted and is putting his own spin on it. The same way Morrison took a GL book starring Hal and chose what to do with it, Waid took a Batman/Superman book starring Bruce and Clark and is choosing what to do with it.