In the String files changed/added for 7.2.5, Mythic Kiljaedan is apparently referenced along with some of his abilities and some pertinent lore about his Mythic phase. Some contacts I have with WF guilds were talking about it and discussing the implications.
I posted a couple of days back regarding whether MMO-champ has an organized list of strings added or changed since 7.2.5. Wanna help me look?