...but how to do it right, short of almost a decade's worth of lead-in films, like Marvel did for The Avengers?
I'd love for them to try and push an extremely high prodution quality JLA animation series on something like HBO. Try and make a lead-in animation series setting up the JLA and its characters as a global TV-event. Of course that would be silly, because as of now, no such thing as an international market for TV shows exists really, so it'd be a futile effort, even if such a thing would succeed in the US. Regardless, I'd love to see how that would look like.
IGN has a neat little *what if* article up, regarding this topic, and speculates about a possible Batman/Superman flick, to set things up for a JLA movie - I sure do love their relationship in the JLA stuff I've read and watched.
On that note, what's your favorite JLA-hero, and would you go watch that hero's origin story in theaters?