I don't really play Omok but a lot of people do, and some of them are not fluent with the double 3 thing.. Omok is a Korean version of the Gomoku Japanese game, and none of the Koreans or even @Lilchubbyken himself hinted about this double 3 rule so I believe that removing the double 3 will not be that "game breaking" since it's just a minigame.