The discussion about Quel'thalas and Northrend from the last few pages is quite funny to me.
It seems most people think we get the zones as they were before, just in higher fidelity.
And yet, in the last 15 years a lot has happend that can justify major changes to the zones.
- The Cataclysm: Right after TBC and Wrath we had the biggest event in the story that changed a lot of areas. This event would have also had left its mark on both Quel'thalas and Northrend. Quel'thalas as a landmas could have been split of the rest of the eastern kingdoms continent mass for all we know. Norhrend could have whole areas be destroyed or submerged.
- The Hour of Twilight: Yeah, remember the big gapping old god holes in Dragonblight during the raid? For all we know, Dragonblight could be riddled with holes now that lead directly into Azjol-Nerub.
- The Legion Invasion: We have seen big legion invasions in areas in the Kun-Lai Summit that destroyed settlements, there would be ample reason to believe things also happened in Quel'Thalas and Northrend. Heck, we know from a upcoming tie-in novel for Midnight that there is a legion commander near Quel'thalas doing stuff.
- The 4th War: While the BfA expansion was set in a few zones, the conflict raged across all over azeroth if you read the follower missions. We could see new and destroyed strongholds. More likely in Northrend, but southern Quel'thalas could be more fortified too.
- The rampaging Scourge: During Shadowlands, the scourge got feral and warlords used them to their bidding. The Blood Elves have a race story for that in the old Quel'thalas zone. This too could change a lot of things. Deathholme might be expanded or there are new scourge camps. Northrend especially might have new scourge pockets in zones it hadn't them before.
- Unknown stories of the people of the zones: Both areas, Quel'thalas and Northrend have people who may have changed things up a lot. Quel'thalas got not only the blood elves, but also likely a certain influx of Nightborne, and with both their magical focus they could change the land by magical means. The Amani certainly were not just contained to their area and did nothing for 15 years. Norhtrend has the Taunka, Tuskarr, Vrykull, Wolvar, Oracles, Frostborne, Titanforged, the people of the Argent Crusade and all the people that lived in the alliance and horde cities, and we don't know what they were up to for 15 years.
If i look at that list, i can see big enough changes that makes it possible for both to be: 4 zones, that are yet vastly different to what we have seen 15 years ago.
Edit: And while we got the Exploring Azeroth books, many of them seem to be stuck at the time the zones are currently in. Likely not meant to expand the story in those regions, but explain why they are, how they currently are. So i would think they are not a block for major changes.