They have been doing that with Batman consistently and the last time they did that after Superman Returns (Superboy and the LSH). Of course they are doing it now with Green Lantern (the animated series on the DC Nation block). Rumor has it that there will be a (3D CGI?) Batman series starting next year.
I wouldn't be surprised if they did have a Superman animated series next year as well.
This is how they should make a JLA movie!
A computer animated movie. 3D (optional) CGI Full length, fully animated Justice League movie!
This is how you can bring all the characters to the big screen, Superman, Batman, Wonder Woman, Flash, Green Lantern, Martian Manhunter, all of the big ones for the first film. All the actors would have to do is voice work. You wouldn't have to worry about it fitting into the Nolan films or the characters costumes looking silly or people not knowing about some of them.
You could even get big time actors to voice them.
Bale could be Batman. Angelina Jolie or Monica Bellucci could be Wonder Woman. Neil Patrick Harris could play Flash. It would be so cool. John Dimacio (spelling?) could voice Aquaman.
The budget wouldn't be much of an issue, not like a live action film. Also, the action and scale could be as big as they want it. A full scale invasion by Darkseid could happen if they wanted. Mongul, the Injustice League. Starro controlling all the other heroes. Blackest Night even.
Plus this would separate it from the Avengers films. No crossovers, no live action. It would be its own film, a big fully animated big budget JLA movie!
They could do 3 movies like this too, Shrek has done over 5 movies right? It could be awesome!
They could make the style as cartoony as they want, very stylized. Or they could make it as realistic as they wanted, very rendered. They could even use the motion capture type stuff they used in Tin Tin. Tin Tin is a great example of what the JLA movie could be like, a comic turned into a big budget movie, fully computer animated using big actors like James Bond and Golum and Xavier.