The Rock appearing at next year's WrestleMania is still not a guarantee.
As we reported earlier, his biggest movie of 2013 - GI JOE 2: Retaliation - opens nationwide on March 29th, a week before WrestleMania 29. WWE does a full media blitz in the week leading up to the event.
A source told me that Vince McMahon is optimistic that The Rock can balance his New York-related GI Joe media appearances on the east coast with WrestleMania. These appearances would be theoretically mostly in the New York metro-area towards the end of the first week of April, or the week before WrestleMania. WWE officials are hopeful that they can possibly piggyback The Rock promoting WrestleMania while hyping the movie, getting extra value out of his appearances.
However, nothing is definitively set on this as of now.