So I think the next TES should be in the Summerset Isles.
The main quest would be a massive attack by the sloads and their attempted resurrection of the master necromancer N'Gasta.
edit] N'Gasta (?b- http://uesp.net/wiki/Lore:Second_Era#2E_864)


http://uesp.net/wiki/File:RG-npc-N%27Gasta.png

http://uesp.net/wiki/File:RG-npc-N%27Gasta.pngN'Gasta in http://uesp.net/wiki/Redguard:Redguard "No trust dark Worm N'Gasta. Powerful, yes, is N'Gasta -- But wicked. Soulstealer. Old and evil." — Joto, mage in http://uesp.net/wiki/Redguard:Redguard Someone thinks the http://uesp.net/wiki/Morrowind:Masque_of_Clavicus_Vile is here on http://uesp.net/wiki/Lore:Vvardenfell. Apparently there are many copies of 'http://uesp.net/wiki/Lore:N%27Gasta%21_Kvata%21_Kvakis%21' here on Vvardenfell. N'Gasta was a great http://uesp.net/wiki/Lore:Sload http://uesp.net/wiki/Lore:Necromancy and servant of http://uesp.net/wiki/Lore:Clavicus_Vile in the http://uesp.net/wiki/Lore:Second_Era, and he may have had a wizard's tower here. An agent came to me asking questions about N'Gasta. The agent would not give his name, but I have learned he was in the employ of someone named http://uesp.net/wiki/Morrowind:Sorkvild_the_Raven_%28person%29." — http://uesp.net/wiki/Morrowind:Artisa_Arelas, Dunmer Pilgrim
The book http://uesp.net/wiki/Lore:Bible_of_the_Deep_Ones contains parts of http://uesp.net/wiki/Lore:N%27Gasta%21_Kvata%21_Kvakis%21. The necromancer was killed in http://uesp.net/wiki/Lore:Second_Era#2E_864 on the Isle of N'Gasta by http://uesp.net/wiki/Lore:Cyrus the http://uesp.net/wiki/Lore:Redguard, who wielded the Flask of Lillandril.

More lore would have to be written but basically the sloads would be attemting to bring him back as a sort of lich and simultaneously launch assaults on the cities. That is undead would walk the streets at night.
So you start the game once again as a prisoner (i don't think we're gonna break beth of that habit). You are being brought to your cell. The whole building radiates decay. To your left guards cart out half a dozen or so dead bodies. As you watch one of them is grabbed by a hand that jumps out of the pile. There is a scream and then silence. The rest of the bodies rise off the cart.

High Rock and Hammerfell.

Akavir Invasion?

I'd like it to be in Black Marsh and feature more hardcoe RPG with darker/survival atmosphere and a less 'epic' and more localized politics/economics loaded story.

I like the concept of multiple factions having different interests which than translate in a more complex main story.

I liked this in Morrowind as well. You had the Empire, the great houses, the temple and the actual 'evil' sixth house cult that all shaped how the main quest played out. Skyrim was more complex than Oblivion in terms of factions but it was still too short and simple.

So I like the idea of going to summerset and having the sload there. That would be your actual evil faction, but at the same time we have the thalmor, the empire, underground rebelions, various powerful mages that have their own court, etc who all want a piece of the pie. Besides that, Summerset is a gorgeous location. It is also less human, so Bethesda could let their fantasy go wild like they did with Morrowind and Shivering Isles.

Llesweyr. No that isn't spelled incorrectly.

Been there and done that in Daggerfall. I'd rather do a province or provinces not yet covered as their own in a TES series, although TES: Arena did cover the whole of Tamriel.

The Black Marsh!

Valenwood.

Transport in real time and full open cities would be cool

http://www.gamesas.com/topic/1330470-official-beyond-skyrim-tes-vi-5/ to discuss ideas and suggestions for the next game, please use it.