Considering the lack of light/dark elements in this game (we merely have 'unaspected elemental damage'), I doubt he will be a normal primal... PROBABLY an Elder Primal, integral to the plotline (similar to Bahamut). I do not think summoners will ever have access to a Fenrir-Egi, mostly because of what I said regarding the elements... and also because we'll only get new Egis with the level cap increase, and there's already three elemental avatars we've yet to have access to. I could also see Fenrir being added as a FATE, although I hope he will have a stronger storyline than that.