Some other locations might be added, too.
There are certain setups of Orochimaru kill points to make you a strong PvP fighter. A large amount of hitpoints will also help you very much.
Also note that there are players who become sitters who are incredibly strong in PvP.
Note: Players with more Orochimaru kills will also be stronger than players will less Orochimaru kills in a battle. For each more Orochimaru kill one player has over the other, they gain +1 attack and +1 defense for the battle. Example:
Genin Sasuke with 2 Orochimaru kills(15 attack, 15 defense) attacks Jounin Naruto who has 8 Orochimaru kills(18 attack, 16 defense). Jounin Naruto will gain +8 attack and +8 defense 'just for the PvP, making Jounin Naruto's 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.