My guess : the Man in Black. We'd have his whole backstory : what is he exactly ? was he ever a man with a "crazy mother" ( I'm still not buying it ) ? How was he trapped on the island ? Normally I'd have seen a Jack-centric closing the show on a full circle, but the title of an upcoming episode I won't tell here leads me to think we'll have another Jack-centric before the finale, and THREE Jack-centrics for such a short season seem too much. My other guess would be a collective centricity, à la Exodus or The Incident. Any ideas ?