Comingsoon.net has a few details about the push-back via an interview with director Jon M. Chu. Yep, it's going to be in 3D (le sigh):
“That was a crazy time,” Chu laughs of the delay. “I didn't want to answer any of the crazy rumors that were happening. The reality was the 3D… “
Among the theories formed about the delay was the rumor that new footage was being shot to include additional scenes for returning actor Channing Tatum.
“We didn't go and reshoot anything,” Chu continues. “I'm not going to say what happens to Channing in the movie, but there wasn't any of that crazy stuff. We just ignored it. It was funny, though, when that new trailer came out. Everyone was like, 'Oh! He's in it way more!'”
“I really wanted to make the second film more grounded to get a greater sense of grit,” he explains. “The action pictures I've been involved in are ones where, when a guy gets punched, you really feel the punch and when somebody gets shot, you really feel the shot. When Jon came in, that was one of the things he said to me that made me go, 'Okay. We're really going to do this picture together.'”