That's one way to go, but the truth is I think that Wonder Woman, Flash and Green Lantern already have a lot of backstory and mythology of their own to have to explain all in one movie, especially if you are going to have them all meet and team up with Superman and Batman. Someone would inevitably get the short end of the stick, backstory wise. The JLA was created as the first "All Star" super hero book; in other words, all the main stars were already household names. No other super team can boast that, not even the Fantastic Four or the X-Men. I think the spirit of that concept should remain, and the only way to really insure that is if the other main stars, namely WW, Flash and GL, have their own films first. If you introduce the secondary Leaguers first in a JLA movie, there will be less appeal for the general audience to see a later spin off solo film. Why is Joe Six Pack on the street going to care that much about seeing a Flash movie when he's already seen him in a movie with all the big guns in it? I think that Superman and Batman may be the only two members iconic enough to be immune from this ( especially Batman, who kind of exists in his own little corner of the DC Universe ) This is all just my opinion of course.