Up to now, Greatturn has been launching a new game almost every month, so everyone has the opportunity to join different kind of games.
Also, everyone is free to publish the polls that can make a better game for everybody.
Players like XYZ sometimes make a scenario game to be played here. It is just another way of playing the game. What happens with it is that the settings are less adaptable by the players, as a scenario must have some "fixed" settings and even special rules in order to work properly.
You don't need to know anything about the history of Africa to play gt10 nor knowing about game of thrones to play gt11, though you may enjoy them more if you know them, of course.
Anyway, those players who don't want to play a scenario game can wait for a GT12 or another GT11 game, as it has been done with GT10 to content more players.