Has anyone made notable progress on these? What of the 5 billion game breaking bugs in the CK and limitations of other software that prevented everyone from having any success at all in doing these things? Have they been fixed?

Been away for a few months, so I don't know the status of modding.

http://www.youtube.com/watch?v=7gJiVKpLPYw&feature=youtu.be you go
So basically yes, as far as I know it's possible.

Well, it takes a lot of time to make new world mods, you have mods like Falskaar who use Skyrim assets and by that creates a new land that looks exactly like skyrim... then you have the new land mods that makes their own Meshes, textures and music, they takes a lot of time to make.

Thankfully someone thought of this a loong time before Skyrim was even announced and begane preparing new land mods for a game that in theory didn't exist, that would be the Beyond Skyrim Province collaboration. You know, lot of Province mods mods for Oblivion was never released, a bunch of them are planning to finish in time for Skyrim, including High Rock: the Direnni West and Beyond Cyrodiil: Elsweyr (now known as Beyond Skyrim: Elsweyr)

So i recommend checking out the Beyond Skyrim province collaboration, not all of the mods are old Oblivion mods that aim to release for Skyrim, there are a bunch of new names there as well, including, Return to Morrowind and Issgard.