3) Forever Evil
When Earth-1 was invaded by the villainous members of The Crime Syndicate from Earth-3, the Justice League was left trapped and the evil doppelgangers of characters like Batman, Superman and Wonder Woman quickly took control of the planet. When it became apparent that this group would ultimately destroy the world, Lex Luthor decided to take action by assembling an Injustice League to take them down, and by the time all was said and done in Forever Evil, Lex was hailed as a hero and actually became a member of the League.
That’s a status quo that would be great to see established in the DC Animated Universe, while this story is definitely epic enough to be told across a ninety minute feature, especially as it would introduce viewers to the likes of Ultraman and Superwoman.