Part of why I struggle to see this happening is that you would need it to be caves, or there is no point. And if you make it into caves then you are really limiting yourself to a specific theme.
You could have a Jules Verne style hollow earth with boiluminescent fungus on the ceiling, or Azerite clusters working as suns, but you would still be in a cave.
Caves always seem to me like a zone you have for drastic contrast, not as a core theme. You go to Deepholm because it's such a drastic departure from other zones, and really make you feel like you are underground. Zaralek as well works this way. You have all these nice zones above for each colour of dragon, and then you get Zaralek Caverns for the Black dragonflight and it really feels it.
- - - Updated - - -
Why do you need to remove the sword anyways? It's been stated several times to not be doing anything. We fixed the issue twice, both at the end of Legion with effective First Aid, and at the end of BfA with all the Azerite.
Removing it would just be for the sake of it, and I would much rather such an event be a big deal. Either by Azeroth herself pulling it out after being birthed, or some other Titan or equivalent doing it.