You've probably lost track of all the various Elder Scrolls mods promising to rebuild particular parts of Tamriel from scratch, so let me jog your memory about Beyond Skyrim: it's recreating the whole of Tamriel in the Fourth Era, when Skyrim is set. The idea is eventually that you'll be able to load up Skyrim and wander wherever you like. It's already released a chunk of Cyrodil, adding the city of Bruma and 24,000 lines of voice-acting, and Chris seemed to enjoy playing it. So, I've got high hopes, and the first trailer for the Morrowind portion of the project does nothing to change that.
If you've played Morrowind then you'll instantly recognise some of the locales, including the giant mushrooms that pop up all over Vvardenfell. By the fourth era, large parts of Morrowind have been destroyed by a combination of natural disasters and, from what I can remember, Argonian invasion. The area that Beyond Skyrim is building is actually larger than the map in Morrowind (which was mainly just the island of Vvardenfell) because it includes all the surrounding areas, like The Heartlands and Velothis. You can see the planned area here.
The team say you'll "lose yourself in the complicated politics of the plotting Houses of the Dunmer, discover the strange and beautiful life that makes its home in the east, or uncover the secret histories that lie beneath the ash". Sounds good to me.
We don't know yet when we'll be able to play our first slice of Morrowind, but don't expect it to be anytime soon. However, the fact that Beyond Skyrim: Bruma exists gives me hope that we'll actually see this come to fruition, which would be very exciting indeed.