I was thinking, since Dragonborn will add a lot of great new resources for modding, including a lot of Morrowind structures and objects, I was thinking that adding the city of Blacklight as a new area to explore would be a really neat idea. It wouldn't be as difficult as a full landmass, as it would just be the city. Perhaps we could make this mod Tribunal-sized. I think we could all try to pitch in with modders, designers, and voice-actors.
If you read here, http://uesp.net/wiki/Lore:Blacklight, it states that the city is the new capital of Morrowind, since much of the land has been taken by Argonians. It's even said to rival that of Mournhold. It has a lot of House Redoran influence.
I want you all to add suggestions if you think you have any ideas.
My ideas thus far:
1. The Rootspire is said to be where the Great Houses now meet, so this could be a major location/part of the city.
2. We should draw up floorplan ideas of the layout of the city, as well as districts.
3. We should add a Main Quest, something lore-friendly and maybe even relevant to the return of the Dragons.
4. Obviously, there will be much use of Dragonborn's new content, but I think we should try to come up with some unique designs as well when using these new resources