Wow this is an incredible idea man! A Blackmoor-style megadungeon - it doesn't get much more old-school D&D than that, and because it's such an open format all member can contribute sub-levels and such at will, like you said. I don't think I'll be contributing (not enough experience to design a really great dungeon), but I can't wait to see the finished project that's for sure.
"There is one good thing about Marx: he was not a Keynesian." -- Murray Rothbard