Build an atom-pc image as a .hddimg, and boot it under KVM. It will hang at udev's "waiting for removable media" message. Interestingly, .iso images boot fine. (probably a low-priority bug as really the machine for running under kvm should be "kvm")
I believe the key here is the image type, not the machine. The image type, hddimg, is a live image and relies on udev to notify when the USB key is detected. We typically boot directdisk style images, or just filesystem images directly. when working with emulation. I agree that this is likely lower priority. I'm actually going to mark this as an enhancement "Support live images for emulated targets". I suspect the image isn't being used as removable media by KVM.
Kevin, See if you can *easily* make hddimg work for qemu/runqemu and if not, summarize the situation to the list and CC Richard/Ross to get some guidance.
I struggle to remember the full context on this but I don't think it's relevant anymore... wic images in my experience just boot in kvms.