Uh, if MOS does get released late next year to box-office success and critical & audience raves -- it will be a great one-two punch for WB. Particularly since the HP series is ended and with the Nolan-Batman series ending next year.
The thing is, MOS went filming with a December 2012 release in mind before WB initially settled on June 14, 2013. From what the mods have heard, the production is still aiming to have the movie completed before the end of next year. I don't see how editing on set and sending finished scenes for CGI rendering is rushing through it. After the completed scenes are fully rendered and the movie wraps shooting, it gives Snyder more time to arrange, trim and refine the movie to his liking. (That can't be a bad thing.)
It means one of several things: 1) WB really likes what they see and wants to have it out sooner or later, 2) Snyder doesn't want to slow down and rather get the movie done in the original timeframe, or 3) One of WB's other holiday 2012 movies is behind schedule and they want MOS as a placeholder in case they want to swap it out.
Anything's possible.