You can see the tweet below:
Justice League #33 out today! Lex Luthor's run at joining the team continues, the Darkseid War approaches and fun chaos w/the Doom Patrol!— Geoff Johns (@geoffjohns) July 30, 2014
Darkseid, of course, was the villain who kicked off the first arc of Justice League (and the New 52 reboot) three years ago. He's also been referenced in a number of Earth 2 stories. It's been widely speculated that, as such, he will play a key role in the war between Earths that has been teased in The New 52: Futures End.
Darkseid's world, known as Apokolips, is also visible on the map of the Multiverse released by DC at Comic Con International: San Diego in support of Grant Morrison's The Multversity.
At the end of DC's recent Forever Evil event, fans glimpsed The Anti-Monitor, arguably the only villain in DC's library more destructive than Darkseid, for the first time since the relaunch. The character said that he was out to get Darkseid, and it's presumably that conflict that will drive the Darkseid War storyline.
Fans have speculated that the Anti-Monitor could be popping back up to acknowledge the 30th anniversary of the Crisis on Infinite Earths next year; if that's the case, certainly starting to tease a story six months out is a good place to begin.
Initial inquiries to DC and Johns were not returned. More on this as it develops...