I am working on a city that exists just past the Skyrim "You cannot go that way" border. Rather than disabling the border like I did in the Oblivion version of the mod, could I have a gate that teleports the player to a point beyond the border? I wasn't sure if the border is a finite blockage or a "the world does not exist beyond this point" kind of thing. Basically, is it once you're on the other side, you're free to roam around as you please?

There's a video out there that shows parts of Morrowind, Cyrodiil, and High Rock/Hammerfell beyond Skyrim's Borders. THere is land beyond it, but I wouldn't suggest going too far out; only White Gold Tower is out there, floating in mid-air (since it lacks most of the Imperial City below it.)

Where the border is and where the land ends are two seperately established things.

You could simply expand the border region (Go to World > Regions, select Tamriel then BorderRegion) to allow the player to walk to your new area as well. Though I believe this would conflict with any other mod that also edits the border region. (Possibly including DLC?)

I've been across the borders a few times. It was a ghastly sight. There's a cell or two of more or less semi-detailed terrain along the edges of Skyrim but it ends quickly. It turns into early-90's Nintendo-quality garbage. There are huge gaps in the terrain. It is not usable in its present state. It would have to be replaced. It is nothing like the terrain that surrounded the playable area of Cyrodiil. I used to roam outside the Cyrodiil border often because it was pleasant and relaxing. I would never do the same thing in Skyrim.

So if you're asking whether it would be better to use this land or create your own (in a separate world space), I would say create your own.