UPDATE
The event may be taking place this Saturday (august 4th). The SOE Fan Faire is going to be happening this weekend and they have a room scheduled with this message.
6:00 PM – 7:30 PM Top Secret PlanetSide Play Session - Details to be announced – Reserve a spot! Game Room Brasilia
This was taken directly from the SOE website by myself so I believe it's legit. The fan faire is in Las Vegas, Nevada so the listed time is PDT. SO this will be 9:00 to 10:30 P.M. for us EST'ers.
People have been guessing that the devs and people at the game room will be playing the 4th empire. But still there has been no official word from the Devs or Mods about this even being THE event so who knows.
If any further info is posted I'll let you know.