Pi Lasagne

I think this is the kind of chip the active inner parts of the sandwich would need:
http://www.microchip.com/wwwproducts/Devices.aspx?product=LAN9514
and their demo board for this
http://www.microchip.com/DevelopmentTools/ProductDetails.aspx?PartNO=EVB9514
is pretty much what it would need to contain, but with a different arrangement of connectors. This chip has a USB hub as well as the USB to ethernet converter and the Ethernet hub, all in one component, so the single PiZero USB could fan out into say two USBs exposed on each layer and the ethernet. Only connectors are needed in the bottom layer, and the top layer is just a plastic slab.