Most Morag Tong members are of the dunmer race. Dunmer like other mer races, are very long lived.
So I don't suspect there is any rush to get back together just yet. They could reunite at any point before TES VI.

No reason the Dark Brotherhood can't be around 200 years after Skyrim. That being said, I'd love to see the Morag Tong again. But of course, that all depends on the state of the Empire.

Peeps may hate me for saying this but I kinda wish they combine the Thief Guild with the assassin guild.

Why can't they just make a purely evil guild, the "we don't kill" that the thief guild have don't really make them any better.

I'm going for the Morag Tong, we know they'll becoming back through certain dialogues and its also a fan favorite faction.

I am completely dissapointed in the DB they shouldn't have gotten rid of the Morag Tong. (I read way too much lore articles on UESP )

I don't understand wyh everyone likes the MT
Boooooring

Yeah, but IMO they can't just leave the Shadowscales in the state they were at the end of Skyrim (even though they might). IMHO, the Shadowscales were just a stub in the lore that had a lot of great potential to grow into something cool and interesting, but instead they opted to use it for NOTHING (with the greatest emphasis on NOTHING) more than just a flag to indicate that a certain character was merely just a disposable character who's only purpose was to act as a filler to make the sanctuaries a little more populated until the point of the story comes to kill them off so they could be replaced by three generic DB recruits (whom none of which would be Shadowscales), and with Skyrim they decided that they would just go right ahead and completely and thoroughly write them right out of the lore again like it never even happened.

Additionally, there's also people that like to RP as Shadowscales, yet in both Skyrim and Oblivion it is not possible for the PC to be recognized as one, and any Argonian PC in the DB is just simply supposed to be a normal DB assassin.

They could go right ahead and write all the lore books they want to flesh out what the Shadowscales were exactly, and every detail of that order when it existed, but that alone would never change the fact that they still used it only to indicate that such a character was nothing more than just cannon fodder for the plotline, and TBH, if the next TES game does the DB and maintains the fact that the Shadowscales are gone forever, never to exist again, I probably wouldn't even give a crap about some lore book that finally fleshes out the Shadowscale lore (unless of course it's because I would want to mod them in), I mean, if this is the direction they are dead-set on heading for the Shadowscales (no pun intended), why should I even care about that? It would just simply be modifying something that was just used for an excuse to make certain disposable characters seem cooler and more important than they really were, not that I don't like any of the Shadowscale characters, mind you, but it's basically what it boils down to.

That said, if they do decide to go ahead and do Black Marsh next,

I never really understood Shadowscales. If it's everyone born under the shadow sign, basically one 12th of the Argonian population is working as assassins. That doesn't make sense, from an economic point of view.

Well, if TES VI takes place in both Black Marsh and Morrowind (which is the best location for next TES imo), I think that we can see both BD and MG.

Maybe they go trough some very dangerous training, so very few actually make it.
Also, I don't think every Argoninan born under the Shadow HAS to become an assassin.
Not to mention that there is a fair chance that lot of parents don't want their children to become assassins and try to hide the fact that they are born under the Shadow.
Still, that's just my opinion and I have nothing to back it up.

Actually it does say tamriel

If we go to summerset isles, there HAS to be a joinable necromancer cult. I mean, necromancy is extremely common there.

Kinda going off topic but being how common it is, it would most likely just be part of the mage guild. Skyrim don't seem to mind it to the point where they don't even talk about it that much (though I haven't personally completed the CoW yet but based on what people are saying the questline is so short that I doubt it would matter) where on Morrowind it was forbidden and you couldn't get much info about it character-wise iirc.

This also is one of the details that makes this whole background story of the Shadowscales getting wiped from the face of Tamriel make no sense. I'm guessing in Oblivion they were trying to say that only certain Argonians born under the sign of the Shadow were actually selected to be Shadowscales, but even a selective process would likely result in a decent rise in trainee numbers each year since they would also have to take into consideration that a certain number of currently active Shadowscale assassins might end up KIA, and others might get inducted into the DB. But like I said, they just simply used it for nothing more than just make disposable background characters seem cooler and more important than they really were, and didn't even bother fleshing out the lore at all, leaving just a stub in the lore that actually does sort of conflict itself in Skyrim in-game lore in some ways if you really examine every reference to that order in Skyrim, though it isn't overly noticeable, unless of course you end up fighting plenty of Argonian DB assassins who, according to their dialogue, are apparently Shadowscales (or at the very least they can be implied to be Shadowscales, since they can say they are like the Shadowscales of old).

Also, another thing too is that the Shadowscales were supposed to be trained as assassins from childhood, so how exactly do they get outlived (and in this kind of business, out-bested since getting killed isn't exactly considered successful as an assassin) by a bunch of serial killers and common murderers (nothing against normal members of course, but still) who make up the bulk of the DB? Seriously, doing this kind of just turned the whole concept of the Shadowscales into a big joke if you really think about it. That being said, I wouldn't mind if they did go back and decide to do more with the concept and flesh out the lore surrounding Shadowscales, preferably if it's more than just simply going "oh, here's a new lore book on Shadowscale lore, they may no longer exist in any shape or form and never will again, you can just read about it." Yeah, as if I'd be that interested in reading lore about a concept that should have been something more than just a bullseye painted into characters' backgrounds to help indicate said characters were going to die at some point in the story.

Of course, much like how in Skyrim they hint at the possibility of having the Morag Tong rebuilding themselves in Morrowind, there are a couple of mild hints that they may decide to have the Shadowscale Order become restored some time after the events of Skyrim,
Finally, need I say that they really need to flesh out this part of the lore better? I mean, there's barely enough lore on this to fill one paragraph. As a matter of fact, I think there actually could be more lore on the Crimson Scars from just one game than the Shadowscales in two.