I am hoping the supposed underground expansion has some steam punk vibes think of Zaun from League of Legends Arcane with a mix of dwarf / gnome technology.
No, don't worry, there are also higher spots but there's still knee-deep water running across them and waterfalling down to the parts at sea level.
Avaloren - I'd love to see this as a land with Azeroth races, yet ones that are so far removed from what the Azeroth we've known has been that they're completely different. Pandaren that are closer to the Pandyr idea for instance. In this, the land would be lush, but in a different way from a place like Un'goro or Sholazar. The capital city perhaps is a different sort of chamber for Azeroth, one from the first ones more along the lines of Zereth Mortis.
Underground - I feel like if we have an underground expansion, Undermine almost certainly has to be the capital. Lots of lore history already, plus the technology of the Gnomes & Goblins would play well with the exploration/Titan themes such an expansion would certainly have. Khaz Algar IMO would be the first raid in this. I'm not sure I see much they can do with all underground zones unless they try to do something along the lines of Labyrinthos from FFXIV. A few zones like that combined with trying to actually get to Azeroth herself could be neat.
World Revamp - IMO, if this is the direction Blizz goes, it should be done as a slow roll throughout the entire expansion. Make it so that we rebuild the capital cities with professions, giving us a new pair of cities each patch. Perhaps the first pair would be Gilneas & either Stratholme or the Crossroads. Otherwise, set a theme for the zones sections to be redone and add in the dungeons/patches to reflect that zone. Perhaps we find a full dungeon under the Sword in Silithus. Capitals would probably be Stormwind or Orgrimmar, though it would be nice to stretch that out to the other cities for once.
Ancient Harbinger
Old Gods, like Y’Shaarj, enjoy arriving in terrifying style, and no one portends their ominous appearance quite like the Ancient Harbinger. This super cultist specializes in beckoning only the mightiest of Tavern denizens. Mere mortals must wait in line to join the party, but the Ancient Harbinger ensures that the Old Gods receive the VIP** treatment they deserve.
That's not even an argument. You presented no actual reason. But it also doesn't matter because whether or not there should be one isn't decided on whether that role can be filled by others, but on whether Blizzard wants there to be one. It's then up to them to create a proper use case or realise they can't and abandon the project.
Your argumentation is irrelevant to the case.
By the way, did we discuss the Kobold with the candle at any greater length? The one Towellie posted a while back, I mean.
Because this video from a couple of years back reminded me of a Kobold quest chain in Highmountain, in which they essentially use their candles to ward off Old Gods and their minions:
https://www.youtube.com/watch?v=vzepiG51LSk
That particular quest chain might've just been a way for Blizzard to expand on that lore for the future. But as the video explains, Kobols all over Azeroth might have kept up that behaviourism since ages past, even if most of them aren't even threatened by the Old Gods anymore (depending on where they live). It's just what they do, keep the candles lit.
Six seats at the big table. Six hungry mouths. One will consume the others.