I feel like with all these various landscapes, such as a forest, snowy/icy areas, a marshy looking area, and mountainous and volcanic areas, Skyrim will need to be larger than Cyrodiil. I mean, each area, such as the Reach, needs to be at least 1/3, maybe 1/2 ideally, the size of Cyrodiil.
This is a bit of a difficult concept to explain, so let me put it this way. There are around 7 or 8 different regions/landscapes in Skyrim. If Skyrim would be too similar in size to Cyrodiil, it means each of these regions will feel small, reducing the sense of size in the gameworld.
So, to account for each of the regions to be large enough, Skyrim needs to be at least 50% larger than Cyrodiil, but IDEALLY, at least 2x the size of Cyrodiil.
Any thoughts/feelings?
Although it sounds counter intuitive, my vote was for Skyrim to be smaller than Cyrodill. Here's my justification:
Having a larger world comes at the expense of detail. The developers can only add so much detail to the world in a given time window, and when the world is so large it becomes difficult to fill up that space in a meaningful way. When people say that the world could be filled up in an automatic process, it is still necessary for developers to check to make sure that there aren't any glitches; moreover, it takes a significant amount of time and or money to create a program that will create believable environments automatically.
Now, you might ask how it is possible to create a world that is simultaneously smaller than Cyrodill and with sufficiently diverse and detailed environments. Moreover, it may also seem to be challenging to maintain an illusion of realism; each environment requires a significant amount of space in the game world in order for it to be believable. The latent restriction of this perspective is that the game world needs to be internally connected; i.e. it should always be possible to walk from point a to point b. However, if the objective of the game is to be realistic, then this is an unrealistic objective. It is rarely the case that people can cover any significant stretch of terrain in less than an hour. Considering this with the terrain obstacles that Skyrim would have (mountains, fjords, cliffs and ice deserts are just a few possibilities of terrain features that would act as obstacles), the developers are perfectly justified in dividing the game world into disconnected zones with diverse habitats. It would even be possible for developers to create the disconnected zones on top of an undeveloped template for the Skyrim landmass that could later be filled in with mods or official content.
The irrelevance of this topic besides (a game mechanic as fundamental as the landmass structure is already determined), I would definitely prefer a disjoint landmass with a high level of environmental diversity and a realistic length scale to a connected "Disney land" version of Skyrim.