I have a simple idea. I'm not a programmer so this is only a suggestion/request.
The idea is to replace the dungeon exit texture with a 3d model. The model resembles the texture. A short stubby tunnel with a 3d grate at the other end. Just beyond the grate is a screen capture of the outdoor world of Daggerfall. The textures would rotate based on the time of day/year/climate.
It would be even more amazing if the mod created an actual tunnel. However given how some exits are back to back with another tunnel that would be impossible. I imagine a 3d modeled object that sticks out into the room with the depth of say a "dresser". It would consists primarily of the door way "stones" around the oppening and a grate with a texture behind it. Some would be have square openings and others round toped. These could possibly used with tombs as well.
As I said, its just an idea.