The book will feature versions of Superman, Batman, Wonder Woman, Green Lantern and the Flash as redesigned by former JLA artist Howard Porter. One assumes that the "3000" in "Justice League 3000" will have something to do with the Interlac "JLA" that recently appeared on a flag on the cover of Legion of Super-Heroes, which will end its run in August.
Shortly before its cancellation, Giffen left Legion of Super-Heroes, a move that was interpreted by some fans as an act of frustration; if this is the next iteration of that book, it seems more likely it was just to get prepared for the relaunch. While there were some cosmetic changes made to the Legion at the launch of the New 52, they were less directly impacted than most other titles by changes to the timeline, since they were so far in the future relative to the point in time where Flashpoint had happened.
Of course, one look at the red hair on that Flash and many fans will ask: who or what will these characters be? Will any of them be New 52-friendly versions of existing heroes like Donna Troy or Wally West? Only time will tell. One thing is certain; don't expect this to be a bwa-ha-hah a minute like the old Justice League books from Giffen and DeMatteis.