Alright so everyone's seen the last Halo: CEA terminal where 343 Guilty Spark speaks of John destroying his Installation and then towards the end he says, "Oh but what I would not give to have a single company of Prometheans here right now. Oh they would most certainly restore order with their trademark lethality. Although... That would mean He would have to be here too. And without the Librarian around to damper his rage, well... These Reclaimers might almost prefer the Flood." And then the Didact's symbol appears in a flash of light. Also at the end of Primordium Guilty Spark claims to suspect where he might find the Librarian.
What do you guys think their relevance will be to Halo 4?
I believe that the dark, ancient threat could very well be the Didact or maybe even Faber.
http://www.youtube.com/watch?v=Km0kWdxvqqU&feature=related