The Riddler #1 taking over Batman was one of the first I heard, last year.
Then we had The Ventriloquist #1 taking over Batgirl, but that may have been from the current planned story, and it may have changed.
Then we had The Prankster #1 taking over Nightwing, but the same applies.
John Cunningham seemed to hint that Crime Syndicate Of America #1 may take Justice League's place.
And now Aquaman Shrine have stated that Black Manta #1 will take over Aquaman.
Many of the replacement may be the obvious title's big bad, but I was initially told that titles would look for more obscure villains when possible.
And the other question is… which of these titles will continue after September? And which titles will their Villain's Month issue be the final issue… so the real final issue of the title will be in August…?
Let's update this post when we hear more.