I have a pretty far-fetched theory that Fafnir (the god slayer), last of the "low-tier" primals, will be summoned from somewhere near Silvertear lakes after defeating Ifrit, Garuda, Titan, Leviathan, Ramuh, Shiva, and the Crystal Tower. This summoning would ultimately be attributed to the Ascians in an attempt to kill off the Twelve, making way for Zodiark. (This is where it really stretches) We encounter Fafnir opening a portal to "Sky" where he would make his attempt on the gods should we fail to slay him. Upon his defeat, the portal remains open and we, the players, of course wouldn't be able to resist investigating what lies beyond. Appearing in this "Sky" zone we're confronted by the Twelve, under the assumption WE are to bring about their Ragnarok...<FFXI Stuff>...Zodiark = Kirin.

...One can dream, eh?