I have a nice pressure cooker that I use to make soups and chile and stuff like that. It crossed my mind whether it would be a way of efficiently extracting the flavor from the grain bag (instead of just seeping in hot water), but then I pretty quickly realized that I'd be extracting all kinds of stuff that I didn't want in my beer (tanins and stuff like that). So, dumb idea, but at least it never got past the "I wonder...." stage.
The other thing is that all the pressue cookers / pressure pans / whatever I have seen are pretty small, certainly no more than a couple gallons (I'm guessing mine may be a gallon and a half, and it's about as big as I've seen).
So, baker's yeast (from your other thread) plus a pressure pan as a fermenter... I'm guessing that's going to be a pretty, uh, interesting brew...