Most of those prior have mitigating circumstances. Animal Man and Doom Patrol went to Vertigo (though Morrison's Animal Man appears to be the only part left to the character's continuity (LDoAM notwithstanding)), I don't know about JLA, but as far as I know it was never exactly shunted aside, and NXM was done away with by a completely different company.
He was also never put at the helm of the creative direction either company in any of those cases, as is shaping up to happen here. That's something that will give his take on any character a lot more weight. And his stuff on the Batfamily isn't liking to end until he at least stops writing for them, which this blurb implies won't be soon.