I was thinking of something along the same lines but without the stacking and cases. Just a board that is the same size as the Zero but adds the B+ usb hub chip. So adds on the opposite edge four usb and Ethernet. The power and HDMI is passed throw with the hdmi gowning to full side. Be a nice little 'PirateDoc' for setting up a board before it sets sail into it's project.......
(see what I did there) ;)