On July 26th, Beware the Batman and Black Lagoon swap places. I think that's the night Batman goes into the episodes that didn't air on DC Nation. Black Lagoon will only have 6 episodes left. Moving it to 3am suggests they may not be intending for Lagoon to be replaced with another new show. Still, Toonami will have 7 premieres a night.
The curious thing is that Blue Exorcist will only have 3 episodes left when Batman moves up. There're some ideas floating around that Exorcist might rerun on the block, but I think if the idea for moving Batman up for new episodes over shows that are ending, it's strange that they'd move Black Lagoon and not Blue Exorcist too if they were planning to move Batman up again when Exorcist ends. I think that means something else will air at 2am between One Piece and Batman.
Kill la Kill is probably going to be the new Aniplex show for Toonami after Exorcist. It's new, it's popular, it's highly requested for the block, and with the physical releases coming up, they'll want to put it on TV the same way the did with Sword Art Online. Some think KLK couldn't air because of Standards and Practices, but Black Lagoon just ended the arc with the Twins....if that can air, KLK should be fine.
I wouldn't mind seeing Gurren Lagann or Magi though.