I am forming a modding team to start a new project in the massive mission to make all of Tamriel. It is Black Marsh. More info at dark creations.com in the beyond skyrim section then you will need to go to the discussion/recruiting forums There you will see a topic TES V: Secrets of Black marsh. Post that you joined up there. You will need to make a dark creation account to post. I really need help!

someone beat you to it... awhile ago o.o
http://tamriel-rebuilt.org/

I guess the difference though is they're still doing all of Tamriel in TES III Morrowind

No, tamriel rebuilt only focuses on making the mainland of Morrowind, nothing else.

This topic would probably get far more interest on the mod forums
There's another Black Marsh project for Oblivion that's in progress, but none in Skyrim that I know of. That said, I don't have Skyrim on PC and thus don't really spend much time looking through Skyrim mods. I could be wrong.

FAQ's

"So, what is Tamriel Rebuilt?

In essence, Tamriel Rebuilt(TR) is a 'mod'(mod is a universal abbreviation for 'modification'. Thus modding stands for 'modifying', and 'modders' are 'modifiers') project for Morrowind and Oblivion, one that attempts, province by province, to eventually create the entire continent of Tamriel province by province as presented by Bethesda in its previous Elder Scrolls titles. Eventually all of the nine provinces that comprise Tamriel will be playable in several or all of the Elder Scrolls games, starting with TES:III Morrowind. Tamriel Rebuilt was founded in 2002 by Ender, before Morrowind was even released. It's standard of quality and dedication to excellence makes it one of the most critically acclaimed mods of the Elder Scrolls community, for both Morrowind and Oblivion. It also plays host to an impressive repository of must-have utilities(The Name Generator is one of the most popular tools of the community) and comprehensive, thorough tutorials on all aspects of modding."

Hint hint, it's called TAMRIEL-Rebuilt, not Morrowind-Rebuilt.