It'd make some sense strategically. Man of Steel 2 is too good an opportunity to waste in terms of at least introducing the Justice League characters. Then, going directly to a Justice League movie would probably maximize box office and better support the stand-alone hero movies that might follow. Warners might feel more comfortable scheduling a couple of movies a year starting in 2016.
If they came out with a big annoucement in the next few weeks, and it included big names like Denzel Washington, The Rock, Josh Holloway, maybe Cranston or Phoenix as Luthor, the publicity and buzz would be enormous.