Separate Emerald Dream expansion has been something that players have concepted and wanted. It just might work and deserve attention on it's own, if it was just thought out in this scale.
My conclusion is mostly based on the fact that Blizzard themselves stated that they won't do an entire expansion of just green stuff, they'd rather just do it as raid tier. Azshara and Xavius, South seas and the bottom of the sea, naga, N'zoth, Neptulon all just tie up in so many ways in the lore and WoW history this would have been a perfect opportunity to include it. Also in addition to other naga and sea themed classic dungeons this would bring up Temple of Atal'hakkar as a possible redone, since it's linked to the Dream.
But all in all this suggestion was more a way to introduce Xavius to the side of Azshara, which was my main point, not necessarily link Emerald Dream so much. Just going deeper into the highborne lore and how and what happened to them. There's plenty of books about it, but doing thing in-game is a whole other thing. In that sense Draenor has been nice to meet a lot of these old characters that have been already gone, and experiencing things that have happened and not just a Caverns of time 20 minute dungeon. Even though Draenor is it's own timeline and things don't happen as they happened before.
This also leads to the Tomb of Sargeras suggestion, i have to admit i'm a little lore obsessed about it.
It's just something i see as the main point how we'll get in to Sargeras and the legions invasion.
Specially seeing how Gul'dan currently is turning up, it just makes me believe even more this is his destiny and Blizzard is actually working on this.
It's going to be a major bummer if Gul'dan is killed as a scenario quest or even as Draenor last tier boss.
But it's true that there's so much stuff related to the Dream this would just be touching the surface and probably not enough for players enjoying lore.
More of a way to not get too deep in to the green stuff and get the subject matter dealed with.
And you're using the 4 patch system, which is personally much more favorable than the current Blizz 3 patch system.
Hence the idea for yet another troll raid, and Zandalar and Hakkar pretty much go hand in hand more than Hakkar goes with the Emerald Dream although there's a connection. I just liked how the previous troll raids have taken the player away from the burning issue at hand and the main point of the expansion for one patch and offered something else, raid's that have been really entertaining. Especially being a more minor raid than the bigger tiers, excluding Throne of Thunder, but ToT had a mix of trolls and the mogu empire as set up which made more sense to be a big raid.
As for the redone dungeons, i actually see them a good thing. It sounds like recycling, but when done to heroic they are also reflected and update as low level normals which are then projected to the current state of the world while leveling. Characters that have actually lorewise died, get removed. Only bad thing about it if you're really into lore and have just started the game you'll miss content that was there. I personally started in TBC and have always felt like i missed something when i didn't get in to 40man curve, things that have been removed Naxx40 and the Bang the gong event. So the redones are not a necessity, but a nice update to the old continent that gets outdated unless Cataclysm like events reasons an update.