As for the original topic of this thread.
I wouldn't be opposed to such a contest because it might just present something new and original. Never know. But I don't think WotC would do such a thing. It already has plenty of settings to revive if it so chooses.
As for an adventure contest... their is one going on right now and we are all first tier judges. It's called the DMsGuild and has been operating for a few years now. By purchasing, rating, and reviewing adventures and content we are all nominating to WotC concepts and authors that we think should make official products. And guess what? WotC then reviews those periodically and pulls in new talent from the Guild creators. Some they bring in for mapping, others for design, and some they name "Adept" and give them a psuedo-official license to create add-on content.
IMO, it's a much better long term method than any event based contest.