I like the first three ideas. We have a robotics and programming forum, so those areas are covered pretty well, IMO.
The dumpster dive section could be fun. Maybe some of us could take apart everyday items and outline (with lots of pictures) what can be found in them and how to remove it and what its worth saving for.
The fabrication section could be interesting also. Not sure how many would contribute though. I made a large air variable capacitor I could add. Might be fun to see some home made or rewound transformers.
I am not sure how we could compile a list of suppliers. The forum is a world wide thing, so i suppose it would first have to be broke down by country, then possibly some of the major reputable suppliers could be listed and a breif description of what they sell? Like I say, I don't know how this could be done well.