Every shoe is different of course, but my mens size 12 Asics Gel-Kayano running shoes fit just fine in either of the frontmost divided sections of the WF. And they fit into the small WF packing cube as well. It's a snug but comfortable fit (doesn't stress the bag, or cube) and I usually pack them in first, especially if I'm going to load the bag.
I really, really love the WF. I've got the older version 1.1 which replaced the original sling with backpack straps and it has become my bag of choice for trips of any duration. I never have to worry about overhead bin space when traveling by air, and can leisurely board knowing the WF will slip under the seat.