As I said in my last post, I'm a big fan of the Wilderlands of High Fantasy setting from Judges Guild. I also loved the old Arduin setting by Dave Hargrave. Both of these settings were classic fantasy settings created by big fan readers.
In the old days, we didn't have the kind of exclusivity of setting you get nowadays -- you could easily imagine Luke Skywalker setting foot in Middle Earth and going toe-to-toe with Elric and Stormbringer, or some other gonzo conglomeration of properties. Eventually, the lucrative aspects of licensing properties became important to the rich guys, and they made it difficult to create this kind of thing. But for a while, you could see it happen. Anne McCaffrey's Pern series got this treatment a lot; if you've ever wondered why they never did a movie or TV show, it's probably because they saw that licensing the property would not be exclusive, since Anne was nice to her fans and let them semi-officially publish derivative works.
However, now we have the Creative Commons, and can be assured that, if it seems profitable to publish, you can eventually get some return for your investment. That being said, I worked up some supplementary material for my submission, the Wilderlands of Dire Omen. It seems a shame to do the work and keep it all to myself, when I don't see it being immediately useful to me. So, I figure why not share online? If it makes my submission that much more useful to others, even better!