According to The Wrestling Observer, the currently discussed main event for WrestleMania 30 is The Rock vs Brock Lesnar. Paul Heyman recently teased a "Paul Heyman guy" could face The Rock at WrestleMania 30 when he Tweeted "boy do I have an opponent for him [The Rock]."
As you have seen on TV, WWE has purposely been keeping The Rock and Brock Lesnar away from each other so they can potentially work a fresh program heading into WrestleMania 30.
While WWE strives to break attendance records at the various U.S. venues at which it hosts major PPV events, it will be very difficult for WWE to break the record at the Mercedes-Benz Superdome in New Orleans for WrestleMania 30.
In related news, the all-time record for attendance at the Superdome was set back in 1997, when the college football Sugar Bowl game brought in 78,344 people. A sellout for a New Orleans Saints NFL game is said to be 73,209, however, due to the way WWE sets up its stage for 'Mania, it appears as if capacity for the event is projected to be around 65,000 fans.
WWE tends to exaggerate its attendance figures, however, generally by about 10,000 people, so that it can claim events have broken attendance records.