Morrowind and Cyrodiil exist within The Elder Scrolls 5: Skyrim only as eye candy for mountain climbers, but Bethesda doesn't rule out their use at a later date, either.
Just after its release, there were reports that players could access Morrowind's Solstheim and Vvardfell, and Cyrodiil's Imperial City in the PC version of The Elder Scrolls 5: Skyrim. While the land mass was seemingly all there, detail began to diminish the deeper they traveled within the "roped off" territories. Since then, there's been speculation that Bethesda will develop these into full-fledged territories later on as downloadable content or expansions, and they may be right.
However, for now, Morrowind and Cyrodiil are only meant to serve as eye candy. Bethesda's Todd Howard said that the areas were placed within the game so that when players scaled the highest mountains, they would actually see the neighboring territories. That's right: they exist simply for mountain view eye candy, and for now, nothing more.
"The reason they are there - and I will not say if we are or are not using them in the future - is when we first built the landmass for Skyrim we knew we were going to have these tall mountains," he explained. "And what can you see? We have views early in the project where you can see into the [neighboring] province from the other game. We needed to have something [there]."
He then goes into describing what other players have already reported: these areas really aren't prepped visually for gameplay -- the movie sets and props aren't fully built, if you will.
"It's not high detail," he admitted. "If you walk there, from a distance it's...yeah, the stuff is there. And the thinking is, maybe we'll use it one day, but our larger worry was, I'm going to climb up on top of a mountain and look that way. What will I be able to see there? We try to cover all those angles as much as we can."
As Kotaku points out, modders will likely take advantage of these unused territories now that the Creation Kit is available, if they haven't already. Just one week after the toolset's launch, over 2,600 mods are available in Skyrim's repository in the Steam Workshop, reports Bethesda parent company ZeniMax.