Now that the Avengers is a huge financial success, JLA fans want a movie more than ever. And Warner is probably listening.
Even though the Avengers was a 2.5 hour epic, one wouldn't have a strong emotional attachment to the characters without the lead-in films to Avengers. That's why the film wasn't just senseless action like Clash of the Titans or Transformers or 300.
So it's clear to just about everyone that before a JLA film, there's got to be films for individual members of the JLA. But it's not going to happen the way that you want it to--even if you complain.
The Avengers film did not have all of the original founding members from the comics. Sure you had Captain America, Iron Man, Hulk, and Thor, but there was no Ant-Man or Wasp. There were only five lead-in films. There was no Black Widow film or Hawkeye film.
The Warner studio will probably only have about the same amount of lead-in films. Especially since people want a JLA film asap.
So who do is see getting a film?
Superman and Batman for sure. A Flash Film has been waiting in the wings for a while, and Warner wants a Green Lantern sequel (probably going to be a soft reboot). And if these films are successful and the studio can convince people that a Justice League film is coming--they may bank on a Wonder Woman film. It's the same idea as people seeing Captain America and Thor because they know that it leads to an Avengers film.
So who gets left out? Aquaman. Like Ant-Man, he probably won't have a film until AFTER Justice League.
Who else gets left out? Well, in many interations, the foundation of the JLA is also the origin of one superhero. Usually it's a White Martian invasion that leads to the introduction of Martian Manhunter. But rumors are that Geoff Johns is/would be co-producer on a JLA film, and that he's working on a treatment for the movie right now--probably with his current Justice League run. So no Martian Manhunter until AFTER Justice League, but Cyborg IN Justice League. That gives us a six-person JLA not including Johns' A.R.G.U.S. agents.
And before you say anything--just remember that the Avengers while not 100% true to the comics was close enough to be good. And Warner Bros. doesn't have a love for their characters like you do--they just want to cash-in.