The more I think about it the more I convince myself that a Justice League film will never work.
Darkseid would have been good, but problem is they'd be competing against Avengers for big cosmic enemy and it'd seem like even more of a rip off by potentially featuring the Apokolips wars with Steppenwolf doing a Loki thing.
Thing is, most of the DC heroes just can't translate to the big screen for a worldwide audience. They work in comic form... Look at Green Lantern. The CGI alone made it look cheap, as for the rest of it...

Why don't they get someone like Geoff Johns, Grant Morrison or James Robinson to write the script? They know the character and have plenty of experience with the storytelling. Not that Grant needs much more of an ego boost mind.