I can't really see it.
Since Pandaria / WoD, they've set up the next expansions' storyline in the current one. Garrosh led to alternate Draenor, Guldan and his pact with the Legion led to, well, Legion, and the sword of Sargeras / Azerite / Azeroth being wounded set up the Horde-Alliance conflict in BfA. Sylvanas being power-hungry and making unsavoury deals first appeared in Cataclysm and was more prominent in Legion, with her storyline in Stormheim and the Valkyries.
Going by the current state of lore, and the story of Shadowland, I think it's more likely the next expansion is something to with the Dreadlords. They're being set up in the Korthia quest chain as these great manipulators who have been the puppetmasters behind just about everything that has ever happened in Warcraft lore. Assuming that part of lore hasn't been retconned, they are what drove Sargeras to madness and led him to create the Burning Legion, which in turn led to the creation of the Scourge and the Lich Kind etc.
There are also hints in Legion and Shadowlands that the Light, or at least the Naaru, are maybe not as completely benevolent as we used to think. It's probably wishful thinking, but I'd love to see something with a conflict between Light and Void that is a little more nuanced and interesting.
Zereth Mortis would be a great ecuse for an old world revamp, but I don't think it's likely. It'd be so much work, and subscriber numbers for WoW are not what they used to be. Also, a lot of it would be low-level content that most players don't even go to see, especially with the new levelling system. It's probably cheaper to add new zones for expansions.
But dragons? There's been nothing about the dragons in Shadowlands. The only one was Ysera, and she's pretty much stuck in Ardenweald now. Also, didn't the dragon aspects lose / give up their power at the end of Cataclysm to defeath Deathwing? With the kinds of cosmic forces we've faced since then, the power of the dragon aspects actually seems fairly minor.