DC can do it but a JLA movie would be years away from now and they'd have to set-up characters the same way Marvel did and, like you said, it'd seem like a retread of Marvel's actions.
Problem is they'd have to have good movies to setup their JLA characters. The Nolan/Bale Batman universe is out since it's over with TDKR and has stood alone.
This leaves the upcoming "Man of Steel" which may end up doing okay but that's a year away from proving one way or another. The next Batman "reboot" series of movies would have to follow in Man of Steel's footsteps in staying somewhat consistent in tone and in establishing a single "world" and itself work out well.
Then we've got the two "big" DC heroes for a JLA movie. Now a DC-CU has to establish more DC characters to put in a DCU and the ones they'd have to do to make it worthwhile is probably Wonder Woman and Aquaman.
Getting a Wonder Woman anything has been a mess over the last few years and, again, they'd have to make a successful movie that keeps in tone with a building universe.
Aquaman could also be done but now with him you'd have to overcome a lot of pre-conceived notions about him and his abilities that are out there thanks to "Super Friends." I think AM could be done but it'd have a lot to overcome. With Aquaman you could also bring in a secondary with Mera.
Then there's Green Lantern. His movie hardly set anyone on fire as it had mixed reaction. So it'd either need a Hulk-like soft reboot or a sequel to do "damage control" and to better fit with any tone the other movies tried to establish.
Being much more a DC guy I'd love to see a DC/JLA movie but, man, it'd be several years away and that's assuming DC has a plan now and can execute it well. They'd have to have good writers and directors set-up.
This is what Marvel did very, very well. They took comic book characters I didn't care about and gave them all good movies. I pretty much got drug to Iron Man and ended up loving it. I found Thor to be lame and just way "out there" and ended up liking the movie, I find Captain America to be way out of time (we're hardly "Rah! Rah! Go America!" anymore these days) and also pretty lame (let's face it, he was pretty much a WWII American-propaganda machine) and he had a great movie. Hulk had two lame movies which I chalked up to him being a character that doesn't work well on his own in a film format with how Marvel wanted to use him.
Marvel took all of these characters and made great movies for them and really established a universe. They did it with great writing, casting and directing.
WB/DC could do the same thing but they might need to really examine how Marvel did it and then try to get as close as possible without trying to duplicate it. Because if they try and to duplicate it they'll fail, it'll come-off as a rip-off.
They need to try and do it on their own way, make a coherent and cohesive universe and they need to start it now. And with any luck, we'll maybe have a JLA movie and Avengers 2 in 2016.
Pretty much agree there, but I'd add just one thing. What made Avengers work, (and I haven't even seen the film yet), is that each of the set-up films connected in someway to show that each film established each hero into this time-line as opposed to say using the original Ang Lee Hulk movie. Without connecting each film, usually by showing a Nick Fury appearance, the Avenger film may not have worked so well.
The problem DC has is that they've behind on the film front for a LONG time. I mean, what characters have they done? Batman, Superman, and last year's Green Lantern? Not exactly a large track record. And none of them tying into one another. Each JLA character needs a rebboot film (or 2) to establish a connected time-line/universe. Otherwise you'll just have a bunch of disconnected and discombobulated films that have nothing to do with one another. That being said, is that why has each Hulk film had a recast of Bruce Banner? Was Ed Norton not available this time? Not that the new guy is bad or nothing, but even he has joked that if there's a new Hulk film that he can't guarantee that he'll be Banner.
Oh, and one more problem with DC-CU is that most of their characters have some sort of F/X superpower. Not saying that that anything isn't possible with today's CG technology, but how do you not laughingly do something with The Flash? This is kind of why DC-CU has worked better in the animation realm. Hell, I wouldn't mind seeing a CG animated JLA series akin to what has been done with Clone Wars, but with slightly more realistic looking character designs.