>Maybe there doesn't need to be any official apparatus in place
>to support this, and individual would-be staff members can
>just decide on their own whether to start work on an area
>beforehand or not.

That's the direction I would lean. No one is stopping anyone from coming up with area ideas and putting them on paper. But if you don't get accepted to heroimm, or if you are but the ideas aren't accepted (Ruins of Galadon!), you might have wasted your time. If you're smart about it, though, you can still come up with a unique core idea, get a bunch of descriptions done, and then probably figure out how to fold it in to your heroimm area project with a few hours of edits.