Black Marsh and Morrowind (without Vvardenfell, maybe?)
Elsweyr and Valenwood (and potentially Alinor)
High Rock and Hammerfell (maybe main quest takes you to Yokuda)
Or come totally out of left field with Akavir
It'd be interesting to see how the An-Xileel govern Black Marsh. From what we see in the TES novels they're pretty much the Argonian equivalent of the Thalmor: Argonian supremacists who don't hesitate to ethnically cleanse "Lukiul" Argonians (those they view as "tainted" by Imperial culture).
As Titus Mede I said: "They are entirely nativistic in their views, interested only in purging the former colonial influences and returning Black Marsh to whatever state they imagined it had been in before it was ruled by foreign powers."
Since the An-Xileel didn't hesitate to use the Lilmoth Hist to control the minds of thousands of Lukiul Argonians and send them to be slaughtered by Vuhon's undead army, they're very brutal and uncaring rulers.
My bet: ESVI will take place in the Argonian-Dunmer war, you'll be able to choose your side or remain neutral and won't look like a Skyrim spin-off somehow
As much as I would love to return to my homeland in the next Elder Scrolls games, I would like to point out that Black Marsh is not a very hospitable place and anyone who isn't argonian would not make it very far.
honestly, blackmarsh would be fun to play. with the ps4 and xbox1 having processors strong enough to be on par with computers (they practically are computers, hence pc games being remade for consoles), id say that it would make for an interesting experience, and i think Argonian accounts said something about migrating village clans, and other scavenger argonians, i think that would bring in options like much more backwood roads and hidden paths, all in all, it would be a nice challenge. and about the disease thing, while blackmarsh is filled with diseases, there would of course be many types of potions, you see argonians in skyrim working at windhelm docks, youd be right to assume nords or khajiit could live in blackmarsh, with them being overall hardy and adaptable.
Also, you know how in the oblivion crisis the hists supposedly improved the argonians to fight off the deadra, what iff there was some sort of xp like mechanic to let the hist improve you like maybe wings (not flying high or anything because that would be to op maybe like the wings for vampire lords), venom or maybe gills (for non argonians, that would probably be available very early on)
I think Blackmarsh would make a great setting. We know that there are ancient argonian ruins, and those could act like the aylied and Nordic ruins of past games. It would Lao be cool if you had the choice between siding with the dunmer slavers or the argonian s and that would affect your disposition with the argonian sa for the rest of the game. There could be primitive argonian tribes that would attack you on sight if you sided with the slavers or could be your followers if you drove the slavers out. I think there should be at least one imperial city since it was an imperial (maybe on the coast with a port) province. This would be the only major city and the rest of the province would be slavers camps, ruins, and small tribal villages, along with the normal caves and random little details Bethesda likes to throw in. Just a thought.
Also, horseback archery. Lets go. We need it. If we could have it 1998 in Zelda on the N64, we can have it on Xbox/ Playstation in 2020 for TES
We can already use archery on horseback. It's my prefered method of slaying giants (and dragons) now that I have my mighty unicorn steed. :3 What we don't have is magic casting on horseback. :'(
If any Elder Scrolls game was set in Black Marsh, I'd want it to have an insectoid hive mind that in order to survive and be released from the hive, they'd have to feed in the name of their broodmother, and beetle-like creatures that make large corpses (think, human scale) and then proceed to burst out of said corpse, becoming large butterflies.
I'd really prefer to see all of the human provinces first, however, rather than just skipping ahead to the weird and wonderful.
I made a small mistake in writing my reply.
The herbivorous beetle like creatures wouldn't create a corpse, they'd make one their cocoon. Slightly grotesque, but then so is everything in this swamp.