You're right though that it is fun to speculate though - I wasn't trying to dissuade you from theorizing that, really I could have been a little more delicate with my earlier post. I'm really sorry about that.

As for the possibilities of an ice Primal, Shiva was already confirmed as a Primal for the game ages ago (images were shown on the developer's blog of her in-game model during the early rendering stage), so it's entirely possible she'll be added sometime this year, if that is what the journal entry is indeed hinting at. Mateus on the other hand... considering Belias already has appeared during the SMN Job quests as a palette swap of Ifrit-Egi, I'm liable to believe SE will probably do the same thing and just use Mateus for a future 'Shiva-Egi' fight for SMN, as well as the rest of the FFXII Espers for that matter.