Some other locations might be added, too.
Also note that there are players who become sitters, who are incredibly strong in PvP.
Note: Players with more Final Tests will also be stronger than players will less Final Tests in a battle. For each Final Test kill one player has more than his opponent, he gain +1 attack and +1 defense for the battle.
Senior Student Renji with 2 Final Tests (15 attack, 15 defense) attacks Shinigami Momo, who has 8 Final Tests (18 attack, 16 defense). Shinigami Momo will gain +8 attack and +8 defense just for the PvP, making her stats 26 attack and 24 defense.
...is not possible, as the game itself is a server-based passive game, means you start an action, you get feedback. To sync two players and not let them do anything else (one might die, though) is virtually impossible, one might log / time out and produce a deadlock, leaving the other player in a battle with no way out.
The chances of cheating are also too great, so it won't become a new feature.