According to Tetsuya Nomura, changes to world map system may cause slippage.
http://www.andriasang.com/e/blog/2010/02/17/ff_versus_xiii_may_miss_e3/.
Uh oh
"We were hoping to debut it at E3, but we're not sure now."
The slippage appears to be due to some changes that are being made to the world map system. "For displaying characters on the world map, we were originally planning on using the method used by FF#, with a small Noctus running about on the screen. But that didn't look too great, so we ended up switching to the method used by FF#."
Those "#" signs are presumably meant to be the roman numerals of certain games in the main Final Fantasy series, but Famitsu had to block them out. Both Famitsu and Nomura agreed that the change is a major one.
http://www.andriasang.com/e/blog/2010/02/17/ff_versus_xiii_may_miss_e3/.
Uh oh