Yeah Boss Man 
As far as a multi level huge dungeon it would have to be done as seperate levels with a unifying theme. I think it could be done just to do it would lose some portability to homebrews and such. Running/editing/publishing one 15-20 room dungeon is very time consuming believe it or not. So doing more than one at a time isn't viable. I would much prefer the smaller ones than spending the time to do one huge one.
What I would like to see some day is a Town/village versus a dungeon. Maybe a meduim sized town where not every buildingis detailed but all the ones of interest. I could see the contributors creating some cool NPC's and some sort of adventure/story line.
Later

As far as a multi level huge dungeon it would have to be done as seperate levels with a unifying theme. I think it could be done just to do it would lose some portability to homebrews and such. Running/editing/publishing one 15-20 room dungeon is very time consuming believe it or not. So doing more than one at a time isn't viable. I would much prefer the smaller ones than spending the time to do one huge one.
What I would like to see some day is a Town/village versus a dungeon. Maybe a meduim sized town where not every buildingis detailed but all the ones of interest. I could see the contributors creating some cool NPC's and some sort of adventure/story line.
Later