Anybody played Mortal Online?
That game shows how a massive landmass that takes about an hour to walk from 1 city to another with a dangerous environment can be very disorientating and frustrating if you're a low level. I drown from having too much stuff in my pockets to sell, got killed by a Domestic Pig & Gazelles more times that I can count, and we won't even get into having to run from PKers in an MMO that you can kill anybody you want. So, as nice as a very large landmass sounds, I'd like to keep it bigger than Oblivion & Morrowind, but not so much so that it takes you 10 minutes to get to someplace that spawns the lowest level animals without a horse.
A super-large landmass could, in theory, work. But we also have to take into account that Bethesda has much more to do than just make a landmass and let us play, they still need to make meshes for weapons, clothes, armor, characters, architecture, random items, monsters, plants, ingredients, caves, ruins, forts, grass (different than other plant meshes), effects, etc. They also have to record voices for spoken dialogue, plan their story and test everything for bugs; add interesting NPCs, Areas, and Quests; they improved their whole system for a while; they've had to plan where there main quest was going, they've had to test it for bugs, they have to create new & more interesting magic effects/systems, they may have had to improve the fighting system everybody complained about, they had to think of original stories for every NPC, they had to create more lore, they had to create new animations and work on old ones, they had to update their AI, they had to make dungeons complete-able (not to mention if they added something like crawling or climbing, that would take a lot more time), they've had to make more specific Animation Markers, they've had to create different sounds & environmental noises, they've had to make music and make sure it fits the game, they've probably had to play test more often than we've played their games collectively, they've had to run around looking at some real-life references (probably), they've had to figure out the artword/logo/box art that they want, they've had to figure out how they were going to advertise for it, and they still might create even new systems in-game that would take some time to develop. And that still doesn't include all the time they'd have to spend coding the next CS to make sure after they were done we could modify the game and be able to change it if we didn't like something.
We really can't ask for a super-large landmass unless you'd want to triple their work load on everything.
Think of the people doing this too, they can't work for 10 years on a game, they have to release it generally quickly so that they don't lose too much money. They still have a budget, and honestly, they still get bored. They're human, just like us, not some collaboration of gods named "Bethesda Softworks"... well actually, that last statement is arguable.
A very large landmass is possible, but an "Epic and Real-World" Sized game would take too long with today's technology... unless you guys would want everything to be completely randomly generated. Which I'm sure Bethesda would like that just as much as us... which is to say not at all since it would mean no custom hand-crafted world. With little allusions and easter-eggs hidden everywhere.
I think what would make the super-large landmass (whole of Tamriel (not actual-size or anything though....)) work is keeping the provinces very separated. Unlike Oblivion where nearly every quest had you going to each town (and practically
required fast-travel), inter-city quests should be a bit limited and important, while inter-province quests should be
very limited and be part of a
very important chain.
And as has been said, procedural generation will do wonders on many things such as forests, wilderness and house-junk. It's much less time and data they'd have to spend on it. Of course, hand-crafting important parts is a must. But who honestly pays attention to the thousands of trees you pass by when going to the next town?
The more sandboxed each element is, the more hard-content can be created.