I actually wonder about the feasibility of a Lightning / Ice primal. Ravana and Bismarck are two elements each, but their elements sit right beside one another on the sides of elemental wheel. Not only are Lightning and Ice exactly opposite one another, but one is the "polar astral" element of the wheel, and the other the "polar umbral". Whether or not we can stretch the pattern that hard remains to be seen.
I had wondered about whether or not an ice/lightning primal could exist, then got my hopes dashed when I read your post.
Then I realized... There's nothing saying that a group out there can't summon TWO primals at once, is there?