I think they should focus on Marlene. She was in the first game as a spectator, but being so young she wasn't able to participate much. In the ending it shows her watching (SPOILER)the battle between Holy and Meteor, so she has some idea of the outcome of it all. Anyway, the plot of the game is Marlene, now a grown woman (well, late teens) goes on a mission to understand the history of Sephiroth, the relationship between Barret, Dyne and Marlene's mother, and to save the world from the evil wrongdoings of Richard, the son of Rufus and Scarlet (hey, it could've happened!) with her group of slum kids, one of which turns out to be Yuffie's younger sister.

Do you think it could work?