SyFy had the rights, they said. Toonami couldn't get the rights away from them, they said.
WELL GUESS WHAT?!
Tonight, during Toonami's Tumblr Q&A it was revealed that yes, Toonami will air Gurren Lagann starting August 16 at 2 am (EST). Here's the video (which also answers the question of whether DBZ Kai will be edited or uncut, as well as addresses a possible Gundam Wing return):