Thanks for bringing up this topic as I have the same problem, only my shelves are only 17" deep. I'll definitely be watching to see what others recommend.
One idea I saw once, but have yet to try is where a gal folded her 1 yard and up cuts onto comic boards and then stood them up in the rear of her deep shelves. In front of them, she placed her smaller cuts of fabric - some were wrapped on half size boards, others were neatly folded, probably like FQ's etc. At least she could see what was behind the front row, but seems to me there would still be the issue of having to possibly move something in front in order to get the back fabrics out. Hmm...