The thing is that people associate the JLA concept with big names: ask a random person to name JLA members, and they'll throw in Spider-Man and Hulk. So, to the general audience, a movie composed of anything other than recognizable characters would probably be a disappointment.
I very much doubt that. as long as the film is well made, most of the general public really won't care who's in it. they'll have questions and will ask those questions in regards as to why certain characters were used, but they won't obsess over it and complain ad nauseum online about how "Aquaman" or "Flash" wasn't used to their liking.
