Originally Posted by
Yzmor
On the speculation side: I don't think Blizz has the nerve to serve the playerbase an entire expansion underground. With the new tech from 10.1, sure, they might showcase some underground zones (though it wouldn't be the first time for them to abandon new tech take Warfronts as an example), but IMHO no matter how well an underground zone is designed, if you never get back up to the surface, it's tiring and depressing. Also the main use of this tech is literally connecting the surface and what's below it, so if everything is underground, the tech is not needed, it would be the same as designing, say, the Broken Isles, but the skybox is just earth, crystals etc. with earthen walls surrounding the borders, like a bigger Zaralek, and that would be it.