Garnet Hill photo
Check out the zippers. The second inside zipper seems to be possibly functional as well as decorative. Even if only decorative, this is a great idea to add some "acceptable edge" to accessories and clothing. By "acceptable edge," I mean adding some metal without looking like a steampunk wannabe. (nothing wrong with steampunk, I actually like it, but it's not appropriate for my work image)
This zipper detail could be accomplished by modifying the pattern to cut pieces and seams to accommodate the zipper detail, or add a godet and insert it with zippers in the seam. As you can see better in the photos below, the Cole Haan bag has a mix of leather with suede pieces behind the zippers. Nice idea.
This could also give your handbag a feature similar to expandable suitcases, allowing you to carry a slim bag most days, but widen the bag on days when you need to carry bulky items.
photos from Garnet Hill
Couldn't you also make unique zipper pulls like this one, with a combination of leather strips, small D-rings, small grommets and metal pieces?