Although the Justice League will be teleported to the 31st century, anything can happen to them, much like what happens in canon Justice League 3000. If you want an idea of the Justice League members, just go to Wikipedia.
The galaxy would probably look like Blade Runner meets Destiny, meets Starcraft, meets Captain Harlock, meets Gurren Lagann.
Races that will appear that are allies to the Justice Leagues are inspired by Mass Effect (Quarian, Turian, Salarian and Drell), Doctor Who (Ood and Judoon), and Starcraft (Protoss)
Enemy Races inspired by Mass Effect (Geth and Collectors), Doctor Who (Sontaran, Ice Warrior, Dalek, Cyberman), Dragon Ball Z (Frieza's Army), Starcraft (Zerg), Star Trek (Borg), Alien (Xenomorph), Battlestar Galactica (Cylon), Metroid (Metroid, Phazon, Space Pirates), Halo (Covenant), and Star Wars (Sith Empire)
Villains that can appear in the series that I picture: Legion of Super Villains, Fatal Five, Blight, Jinx, Killer Frost, Bane, Deathstroke, Poison Ivy, Mirror Master, White Martians, Doomsday, Crime Syndicate, Queen Bee, Dr. Light, Sinestro, Starro, Brainiac, Solomon Grundy, Vandal Savage, Joker, Lex Luthor, Darkseid
