Regarding the 2014 release, maybe they could do it and make it a Christmas release?? That's the earliest they could possibly do it I imagine. Here's a wild theory: they could have been filming both movies simultaneously??? I mean they've been at it since 2011 and keeping it under wraps yes?
I'd love it if we got JLA in 2015. That way my dream of the three way box office nerdgasm war between Avengers 2 vs Star Wars VII vs Justice League might actually come true. XD
But seriously though, JLA this early might work and probably be more favourable(especially with regards to Batman who instantly get butts in seats and as a general marketing opportunity). Just watch from 2:28-2:50.