Not sure it's been written up anywhere, but basically it's the following:
1) Finish all Rhapsodies missions and get the Scintillating Rhapsody KI
2) Go to Reisenjima and check the portal, using the KI to warp to a hidden location with 2 goblins
3) The goblin on the right has some dialogue and requests beads in different increments; 100, 500, 1000, 1, which unlocks his collection of weapon KIs.
4) For 50,000 beads, you can get a KI for the weapon(s) of the job you're currently on. Make sure when you pick this up that you're on the job you want, or else you'll be stuck with the wrong KI.
5) Kill all Gaes Fete NMs in Escha - Zi'Tah. This includes Wrathare and the other "hidden" pop NMs.
6) Kill all Gaes Fete NMs in Escha - Ru'Aun. This includes Kirin and Warder of Courage, as well as the other gods and AAs.
7) Kill all Gaes Fete NMs in Reisenjima. This includes Teles and the 6 new high level NMs.
8) Unknown final steps, but there's dialogue found that has the goblin talking about "goads and fragments". Judging by SE's statements, this is likely some challenging battle content or some minor thing, and not something you farm.
If their statements are accurate, then the only "farming" aspect of making an Aeonic is the 50k beads. I presume that for making additional weapons, you'd begin the process again at step 4.