The last time we played it finally happend. One of our players got the mission where you can join the cultist an win the game by making everybody else loose. I think that Arkham (featuring its expansions) is quite a hard game and that tiny bit of extra terror didn´t really help.
I would like to know if anyone of you favors the idea of bringing traitors in the game. Maybe do an expansion where traitors get some more influence. In our case after the player revealed his treason he couldn´t do very much ... Of Course it would be very necessary to keep the Balance and so the Investigators have to get some new gear ...