Didn't Yoshida mention that the story of the Calamity (aka Bahamut) would end with the final coil?

The main focus of the expansion is not elder primals, it's the war between Ishgard and the dragons of Dravania (as seen in the logo of Heavensward), the main theory so far is that the main antagonist will be Nidhogg, a name you will get to know if you ever level up a Dragoon.