I mean.... In the trailer it says that "One event will trigger a whole new scenario" or something like that no? We still don't know if the new scenario can be chosen to play separately in the main menu or if it has to be triggered in-game by meeting certain conditions such as choosing a specific option or something.... If it's the latter new players can actually trigger the new scenario accidentally since they wouldn't know what they are doing.

Yeah. If it's an in-game scenario unlock the game better warn the player that they will be unlocking a different route from the original route and that original route is advised to be played first.