With the primal getting a lot of focus lately, since they are profiled as gods and ultimate challenges. Right now we have Ifrit, with the Evil Moogle, Leviathan, Garuda and Odin on their way. Carbuncle has also been announced more or less, but more as a summonable pet.

So the obvious question is which summons do you want to make it into this game that haven't already been announced?

Bahamut
Diabolos
Cerberus
Phoenix
King cactuar
King Tonberry
Ixion
Fenrir
Shiva
Gilgamesh
Hades
Moomba
Quezacotl
Valefor