That would be the easiest way to implement it, yeah. Use Episode Gladio's first cutscene to introduce the prompt for his episode, add a quick cutscene between Prompto and Noct in a barracks in Zegnautus to introduce the Episode Prompto prompt, and stick the Episode Ignis prompt right after the big CG scene in Chapter 9. Integrate Chapter 13:2 into Noct's scenario properly, preferably right after Noct falls off the bridge. Build every DLC which has yet to release into the game the way the Royal Pack does. Of course, the prompts should be called "Active Time Events" for the sake of the FFIX reference.