Really i hope not. Its told to be inhospitable for anything but the masterrace.
Also i don't think most people would be fond of talking lizard everywhere, especially because most people i know who are monsters don't love Argonians find them ugly or hate them for other reasons.
And a more personal reason, I like to play as and argonian as my first char and i like to be special. And its hard to be special if everyone else is also a glorious scaled being with strong legs and a shapely tale.
I fully agree that based on lore, it would not be feasable for a non-Argonian to delve deep into Black Marsh, but then again...
Cyrodiil was written to be a giant jungle and we got kind forests and hills. In terms of game mechanics, as some have pointed out, Bethesda would probably just dumb down the true lore and make it possible for other races to adventure within the borders.
I dont care where it is, just give me TES 6 !!
But, personally think Argonia can be made hospitable for the player, with restrictions of course. They can have an inbuilt Frostfall & Realistic Needs kind of mechanic to let you deal appropriately with the harshness of Black Marsh.
Because Skyrim took about four years to complete. Skyrim's one province. Tamriel has nine provinces. If you want all of Tamriel as the map, you'll be wairing a VERY long time for it to be released. It's not an issue of hardware not being able to run it. It's an issue of how much time it would take to accomplish. If the game were to come out in a decent amount of time, all the provinces would be seriously dumbed down, smaller, and lacking.
Quality over quantity.
Yea, I would call BS on the whole Black March thing. However, I have a feeling if they were going to make an Elder Scrolls 6 it would be close to ESO. Reason being this, is that according to some books and people in Skyrim, you have the rebuild Aldermeri Dominion, Redguards, Orcs, and Bretons are still fighting with them (which may lead to a rebuild Daggerfall Covenant), and then you have the Argonians which invaded Morrowind, which mostly is destroyed from the Red Mountain, and much of the Dunmer live in Skyrim where the Nords hate them both. So I don't see a Ebony Heart Pact anytime soon. Could be an all out war. Or even a fight for the throne to become Emperor! Even though Oblivion was shut, the throne was made for a Dragonborn! We'll see what happens if they make it. Personally, I would love to see the Dwemer some how return and you can be able to play one!