The Elder Scrolls is notorious for many things, one of them being the sudden discovery of secrets in very old games, be they combos, glitches, or spell synergies. Skyrim is no exception. After the console commands were published, people started abusing the life out of the NoClip mode to explore things in ways not meant to be. What did they find? The other provinces of Tamriel. Scaled down in size significantly, but regardless it’s in there.
The entire continent is explorable, but lacks in form of flora, fauna, buildings, or features that are worth noting. There are an infinite amount of reasons this could be here. The most obvious ones involve allowing modders to add the older games and areas, because they could, or because Bethesda may be planning to add DLC and expansions to make the entire continent a fully playable colossal game world that smacks all the others aside with ease.
Bethesda loves their modding community, but something like this goes far beyond what I would expect them to do. To have the entire setting in a single game is not something I would expect at all. There is no denying the size of Elder Scrolls games in general lends to its game and impressiveness.
As soon as the creation kit is completed, there is going to be a lot of it hitting the fan in a very short frame of time.