I just noticed this. After several pages where they argue about whether or not he should be invited even though the 2nd edition of the game ruined AD&D, he begins participating in the thread here: http://www.dragonsfoot.org/forums/viewtopic.php?f=11&t=26912&st=0&sk=t&sd=a&start=60
He notes that he tried to license Planescape from WotC a few years ago. That would have been pretty awesome.
As for PS itself, I wanted to give AD&D a real air of fantasy, as in the mysterious and unexplainable. AD&D too often gets into a game of firepower and tactics, but in the planes that sort of approach wasn't going to work when there were so many things more powerful than the characters. So it was downplaying the slaughter in favor of the mystery. The biggest influences were that I'd been reading a lot of experimental fiction, I was getting bored with doing the same thing again, and frankly, some of those exercises in anthropology I'd done hadn't sold all that well. So I was tasked with doing something that would to appeal a bit more to the White Wolf sort of crowd and I just went mad.
That would have been awesome. *drool*