Avaloren is an entire continent, ala Northrend, Pandaria, Kalimdor, the Eastern Kingdoms, etc… It’s not going to be just a zone.
Also keep in mind, it’s the Arathi Empire. An empire would be larger than a single zone.
I imagine Avaloren will be part of its own expansion.
https://www.icy-veins.com/forums/topic/78824-unraveling-the-war-within-story-through-datamining/
There is datamining for a cutscene called “Alleria and Xal at the Waterfall” where Anduin, the player, and Alleria need to jump from a city’s edge into water to escape Xal’atath. Anduin and Alleria may also be the escaped prisoners mentioned in another datamined scene.
As for Dalaran and the Kirin Tor, it’s kind of odd they’re seemingly destroying Dalaran for once and for all and seemingly destroying much of the Kirin Tor faction along with it a year after releasing a Shop transmog themed to the Kirin Tor.
https://www.wowhead.com/news/high-scholars-pack-now-available-500-traders-tender-transmog-334780
I think there’s a possibility that follow up on the decimation of the Kirin Tor will happen around Midnight, being that there’s a recolor of the High Scholar set in red. Alternatively, maybe the red recolor will be used for a model update for Meryl Felstorm? It does have orange gems similar to Meryl Felstorm’s old appearance through the action figure from years ago.
I really don’t know what they’d do with the Kirin Tor without Dalaran, though. They really can’t have this be “Destroy for rule of cool and then forget” like they did with the Skyfire given the importance Dalaran and the Kirin Tor have to the current identity of the Mage class.
There’s maybe a chance for follow up on the Kirin Tor themselves given the datamined “Instructor” sets and some of the datamined civilian transmog sets being in color schemes similar to the Kirin Tor, but nothing guaranteed from any of this at this time.
I also wonder what’s going to happen with the Forge of the Guardian. That getting destroyed surely wouldn’t be good. I’m wondering what would happen to Alodi.
I haven’t forgotten Nazjatar and the Emerald Dream being single zones.
At the moment the Arathi seem like our most likely path to be introduced to the far side of Azeroth. To the beginning of a new storyline/saga as opposed to the end of a storyline. While it could just be some high grade hopium I don’t think it’s unreasonable for people to set their expectations a little higher than a patch zone’s worth of content.
Honestly I’m kind of bored of Alliance stuff, but I am looking forward to seeing more human kingdoms being portrayed. Seriously, you’ve seen the armor sets or the architecture? Badass. I actually want those guys to reclaim their city back in Arathi.
The Arathi armor you can get from outdoor activities does look absolutely gorgeous. I want to collect it so bad for my Man’ari hunter 
The more I hear about Avaloren the more it sounds like heavy foreshadowing and world building. And taking a page from Robert Jordan and the Seanchan from the Wheel of Time.
Also Anduin as a priest has used Shadow, he mind controlled the dwarf in MoP. I’m not to worried about the kidnapping. It could be a short term thing for all we know.
I’m more intrigued by the fish that was found in Hallowfall,
Pretty sure the world of wheel of time doesn’t have a centralized government.
That’s exactly my biggest fear too. I don’t think they’ve considered the ramifications at all. They just want to have an epic cut scene of Dalaran plummeting to the ground for maximum shock value and to generate hype for the expansion without taking into account what it will mean for the game in the long run.
Aside from that, Dalaran and the Kirin Tor are my character’s whole identity in WoW and taking them away would be devastating on a personal level. I have mained a mage since Vanilla, this character that I am posting on as a matter of fact (who used to be human but I race changed when faux High Elves became available). I have played on the Dalaran server from the start and never transferred. Whenever I would go on vacation, travel for work, or just take a break from the game, I would purposefully log out my character in Dalaran (first the bubble, then in WotLK and now in Legion). This place means the world to me and has been a hub for roleplayers for well over a decade now. Taking that away is just cruel and terribly shortsighted.
Yeah sure, the WotLK and Legion versions aren’t going anywhere and can still be visited but it’s not the same. It also highlights the futility of destroying it in the first place when the game’s mechanics don’t even allow for a full removal for maximum impact. That’s how ingrained it has been into the very being of the game.
Lastly, on an unrelated note, as a New Yorker I get triggered by seeing any kind of towers coming crashing down, let alone ones that I have become incredibly attached to. I completely understand that this is a personal issue and it’s totally on me but my lived experiences are nevertheless important factors in how I perceive this. I just wanted to mention it to give context for why I am so passionate about the topic.
I’ve mentioned it a couple of times, but I have a niggling suspicion the Kirin Tor is intended to become a part of the Azure Dragonflight in the same way that the Bronze flight has its mortal timekeepers. The two were already tightly linked in Dragonflight, so they could just go full in on that and call it a day with Kalecgos being their new boss and their HQ being the Azure Archives.
Dalaran was calculated as a loss for sure, because it is the only neutral city they really have to destroy that they did not have plans for but also was tied to everyone enough they would care about its destruction and the people lost in the process. Given this Saga is basically a single story given the resources and time of three expacs, I suspect the ramifications of it will be felt even 6+ years from now in The Last Titan.
I’m not ready to lose Khadgar, i like the dude too much.
Dadghar will be missed. 
I feel like BfA and Shadowlands has had negative effects when it comes to the Undead. The ramifications of Sylvanas getting villain-batted hard damaged a lot of what players liked about the Undead.
They can easily make some of the same mistakes with the destruction of Dalaran and if they try to write off the Kirin Tor as well and damage what people like about Mages.
The Arathi of Hallowfall have only one mage among them, so maybe surviving members of the Kirin Tor will interact with them at some point. It also means that the datamined “Educator” sets are not themed to the Arathi, and so far they don’t seem to be themed to the Earthen either. The color range isn’t wide enough to be Algeth’ar Academy, so some of the datamined outfits could be (and hopefully are) for surviving Kirin Tor members.
https://www.wowhead.com/news/cosmetic-civilian-transmog-sets-from-war-within-alpha-338829
I think there’s a decent chance that they might build a new city at some point or some tower somewhere, but whether or not it would be called Dalaran is up in the air. There’s also a chance it won’t really be replaced with anything as well.
We’re still not really clear on what the ultimate fate of the Kirin Tor is and if a potential replacement faction would be able to suitably replace the Kirin Tor.
That is how you know a death will have impact, as a writer. Losses that matter never happen when you are ready for them, or they would not be true losses.
Ideally it will be rebuilt back where it originally stood on an even grander scale and could be a gateway for updating the entirety of the Eastern Kingdoms akin to what was done with the Arathi Highlands but much more expansive. Lordaeron, both Plaquelands, and the entire Quel’thalas including Silvermoon. It would be a huge miss if they don’t make the Sunwell a focal point in the coming war with the forces of the Void.
P.S. Khadgar and the other Kirin Tor members of the expeditionary forces to Draenor in WoD were able to build massive outposts complete with signature Dalaran style towers in several locations and quite quickly. As did the Kirin Tor Offensive on the Isle of Thunder back in Mists. Almost like they have some kind of portable tower that you just place down where you want it, sprinkle some arcane dust and it grows like a Chia Pet. 
Nazjatar is literally a city. Why would a city be larger than a zone?
As for the Emerald Dream, we’ve only ever seen bits and pieces of it. It’s much more massive. This is like saying the Shadowlands are four to six zones big, when they’re actually much, much more.
A continent is a different matter entirely, though. Connected landmass with varied zones/biomes, and likely different races as well. I suppose it’s possible the Arathi Empire has full control over Avaloren, but if that’s the case then I would imagine within the empire we’d see many different sub-cultures, not unlike how among humans the seven kingdoms have different cultures of their own.
I very much want it to have a whole expansion dedicated to it, but I do wish to point out that this is how many people thought of the Emerald Dream as well, and when we finally got some real access to it outside of a druid order hall or an instance, it was a patch zone.
We’ve only seen one tiny corner of the Emerald Dream. They could easily do an entire expansion about it with a half dozen zones if they so wanted.
We’ve seen what mattered. The Emerald nightmare, one of the coolest things about this, especially if you read Stormrage, was “fixed” the main antagonists were gutted. Now it’s just pretty sparkles and sleepy woodland creatures and that sounds very boring.
Until one of the Life Lords goes on a weekend bender and we suddenly have Life Demons waltzing around spreading Felflowers like felfire.