The Egi Conundrum: Heavensward and Beyond!

[Exodus-E]

As far as I remember Bismarck is water attributed summon (FFVI and FF Unlimited), but in these games/shows we didn't have Levi.
So I wonder, what will they invent for Bismarck in FFXIV.

Here, Bismark doesn't look like he's water-aspected, but rather wind-aspected instead (given he's flying through the clouds).
But who knows at this point...we'll have to see once the actual expansion comes out.

Siren is a lower case primal (An aetheric being), while Diabolos is confirmed to be a void creature.

WRONG. Here, siren is a species of creatures and NOT a primal/aetheric-based being.
You're right in that Diabolos is a voidsent, though (and they hinted at his possible return).