Man of Steel is about 10 days away and everyone is already trying to gage the films box office success and tie it into an eventual Justice League movie. Just today Newsarama broke a story reporting that the movie ticket website Fandango had pre-sale MOS tickets out selling Marvels May release Iron Man 3. The story even goes as far as to claim:
"Comic book readers know the at least immediate fate of a Justice League film is presumed to be hinge on Man of Steel being a box office success and a critical launching pad for a cinematic DC Universe the way the original Iron Man was for Marvel."
The main reason I believe this must come before a JL flick is because it serves as the perfect way to introduce Batman into the shared DCU. All indicators point to Bale being done with the cowl, so bringing in a "new" Bruce to fight side by side with an already established (Cavill) Superman, would be a great stamp of approval, and most likely diminish the comparisons to the DK trilogy.
The next reason I want this to happen is that it offers something Marvel can't. Marvel does not have 2 property's that carry the weight of Batman and Superman and in doing this would limit the detractors that will say that "DC just copied Marvel's formula, how unoriginal, blah, blah, blah". Well guess what? If World's Finest leads into Justice League, DC will have produced a cash cow of their own design and that alone in this day and age is a very big deal.
So be ballsy DC. Don't follow "the formula" and blaze your own trail! Billions of dollars await you.