If Blizzard ever decides to revamp Azeroth again they can use the Infinite Dragonflight as the cause. I am still waiting for Nozdormus downfall and he can definitly be a main villain and carry an expenasion theme, at least as the initial threat.
However, I would actually really like a, so to say, "boring" expansion where we maybe just start to actually rebuild stuff and turn back to some local threats instead of these big cosmic things. Just to let the world and our characters actually breath for a bit. We could of course still have raids and that could be any sort of thing like a Bloodsail Raid, Old God Remnants, another Titan Facilty and what else. Just "normal" things by now.