While Ice / Lightning are the only two elements not represented by a primal in 3.0, I don't think there's going to be one soon if ever. They don't interact with each other on the elemental wheel; conversely, fire / earth (Ravana) and water / wind (Bismarck) do.

Anyway, not much point in speculating since there's a massive array of summons that could show up. Hell, they went with something completely original (Ravana) and a couple that had only shown up once or twice before (Bismarck and Knights of the Round) in 3.0. Anything is possible.

(*Silently prays for Ark to show up as a lightning / fire elemental primal*)