Yeah, more context is needed. I kind of had this tab open for 2 hours unsure of how to answer (and got distracted
)
do you have an existing game, and want to add a seprate story ark?
why are you calling it a story ark? using the example of an episode gallery sounds like a completely different mechanism.
is your game in chapters or something, but you want the player to be able to select chapters?
as for story ark, are you having a particular problem?
other than creating a label and organizing your script files to manage all the writing you may have to do the only technical challenge i could see is if you want the player to progress through a certain storyline but only progressing a bit at a time while they still play the main story line, going back and forth between normal and a 'Halloween special' mode or something.