I got to say...this has got to make some DC fans annoyed at Warner Bros for not making A JLA movie.
They need to make a Superman movie they're actually happy with before they can make a JLA movie.
Honestly if I were DC, I'd first try and Batman/Superman Worlds Finest movie, then go from there.
Avengers did it right. They built the concept from several movies, and only pulled the trigger after every person there was already established or at least introduced. Doing a team like JLA or Avengers is hard... but at least with Avengers they've proven it can be done if you know what you're doing.