From official forums via MMO-Champion:
Players that queue for the Wintergrasp battle and are selected to join will be placed into raid groups upon entering the zone. These raid groups will function similarly to the battleground raid groups with a few exceptions. Players can leave it at any time, the leader can issue invites, etc. The only restriction is that if a player leaves Wintergrasp while the battle is active, they will be removed from the raid (to make room for the player that will take their place).
So.. all that’s missing is that when you queue … the defenders all zone into the fortress (which is locked and no one can get out) and the attackers all zone in at one of the towers (also similarly locked).. and you get a 10 second warning that the gates are about to open.. then the gates burst open.. and everyone runs out.. passes each other in mid field (where they grab tanks) and then the “defenders” stream down and smush the towers.. and the attackers all stream up and attack the fortress.. and um.. wait.. we need a new Drek.. something for us to get distracted with in mid field. I know.. ADD A FLAG!!! YESSS!!! Or..wait wait.. I know if you kill enough elementals DURING THE BATTLE you can get Archevon and Emalon and Konanigon to spawn and defend your side.
The new Wintergrasp Battleground. Totally the same as everything else.