I found what you were looking for!
This blog led me to the podcast link.
Excerpt:
On the latest WOTC D&D podcast, Steve Winter talked about the great
campaign-world books that came out of Second Edition D&D. He said
that, for every kick-ass setting like Planescape or Al'Quadim, they
had a bunch of ideas just as good - they just didn't have time to
print them all. Prompted, he described one of the settings that he'd
never forgotten:
There's one that always comes to mind: it was proposed by Jeff Grubb,
and I forget what the name of it was, but the idea was, it was a world
where there were all these mountain ranges, and all of civilization -
the good part of civilization - has been driven up to the tops of
these mountains, and then there's a tremendously thick cloud layer, so
wherever the sun shines is where good exists. Everything beneath the
cloud layer has been overrun by evil. There are cloud ships that sail
out from these mountain-top cities across the clouds, and the
adventurers rappel down to the world where they go raiding the ruined
cities that used to be down there, looking for gold, metal, and all
the kinds of things that they don't have in these mountaintop cities.
As Steve Winter says, that idea isn't quite as fresh as it was in the
late 80s (he's seen elements in anime, and it reminds me of Final
Fantasy) but I think it's still an evocative and inspiring world. I'm
ready to play it! But, since all we have is a podcast sound bite and
not a campaign book, I'm left with a lot of questions: exactly what
kind of evil lurks in the cloudy lowlands? What does the wilderness
look like?
That blog leads to many interesting ideas, and there are some very wonderful comments there. Unfortunately - it seems that it was never more than an idea, so there is not much campaign setting for you to use in yours. But why don't you be the one to write it?
Incidentally, while searching for your lost podcast, I found some related and interesting things for you to explore:
Update: This story idea has been sitting in my mind since I answered this question almost 5 months ago. I could not resist the urge to use it for one of my games on the new Storium website. Here is the link, so that anyone looking for information about this can easily connect.
