No one knows for sure yet, but I maintain that it it part of a trilogy.
Cataclysm and Dragonflight share so many elements, it's almost comical. Borderline A New Hope and The Force Awakens situation.
- Twilight's Hammer Cult / Primalist Cult.
- Void influence in the background.
- The Dragon Aspects.
- Big focus on the Black Flight.
- Elements and some form of "elemental lord", including cases of non-elementals becoming transformed.
- World tree plays a role.
The list goes on.
Since the other expansions, except for MoP, all seem to be part of trilogies, it makes sense that these two are as well.
It also makes a lot of sense that Blizzard is cycling through the bad cosmic forces of Disorder, Death and Shadow.