I'd think it would be very negligible on the tulle.. The organza I saw was even tighter weave, some tighter than nanoseeum.
Seems to me that if migration did occur, it'd be a) minimal, and b) bi-directional.
Those holes are small, maybe 1/8th inch.. Some quills might move around, but the actual quill free down clusters? Maybe, would it be at a volume to matter?
Just can see it being an issue, although I definitely concede that I'm just speculating.
I'd love to hear if anybody has actually tried it, and noticed any loft change.