"The fact remains that the new guidelines cut capacity of bags by 40 percent."
???
The volume of the current regulation (22" x 14" x 9") is 2772 cu in. The volume of the proposed regulation (21½" x 13½" x 7½") is 2177 cu in. The new bags would be 595 cu in smaller, 21.47% smaller than 2772 cu in. - not 40% smaller.
(For the mono-metric people, the current US regulation, rounded to the nearest cm, is 56x36x23, or 46.368 l. The proposed regulation, 55x35x20 is 38.500 l, 17% less)
If you have a roller with a 14" wheelbase, it isn't going to fit into a 13½" sizer; it the height from wheels to handle is 22", it won't fit in a 21½" sizer. That leaves only reducing the bag thickness to make it fit.
Of course, that's outside dimensions. The inside of the bag is smaller, and the heavier the bag, the more volume the bag itself occupies, therefore the less volume of what you want to carry.
Assuming 0.0412 #/cu in density of nylon and 90% weave density (I'm guessing at this), my 2# 10oz all cloth soft bag probably "costs" me about 70 cu in. A six # roller will cost you more internal volume.