I’m about 99% certain that this will be the next expansion. It just seems like the right time, and the natural place to go after Dragonflight. They’re already developing so many storylines around the Green Dragonflight, that will lead into more later on.
[Spoilers below from the 10.0 storyline.]
Such as the planting of a new world tree, and the return of Ysera.
In previous interviews they’ve said that Dragonflight was already being developed even before Shadowlands launched, so we know they work atleast 1 full expansion ahead of time. (It’s crazy to think that all of the patches for Dragonflight, and everything we’ll see over the next 2 years, is probably almost completely done already.)
I have no idea how they’d even pull off an expansion with such an extravagant theme though. Then again it is Blizzard, and they always find a way to blow my mind regardless.