So now I need to decide:

Hardware addresses

Do I need to buy a MAC address block? Do I need to buy an IEEE address block? Is there any way I can do without either one? The experimenter community should buy a block of each and sell them off in small amounts. Also, they seem redundant. When I have a device with ethernet and zigbee both, I have two nearly identical 64bit addresses. Both expensive, too!

Core component makeup

I also need to decide between a highly-integrated solution (like ConnectOne for Internet and and TI for Zigbee) and something I roll myself using cheap Microsoft parts. My choices now are:

1. Microchip Ethernet controller for the Ethernet solution. Lowest cost I think.
2. Wiznet for the Ethernet solution. Probably most robust, lower code overhead.
3. ConnectOne would be even more robust and simpler (includes DHCP, keepalive, etc), but it would be more expensive.
4. TI would likely be the most robust, lowest code overhead Zigbee solution, but it would be the most expensive.
5. Microchip would probably be the cheapest Zigbee solution, but it would require a micro to hold the stack and do all the work. If I’m lucky, the Zigbee stack could fit in the same micro with the Ethernet stack.

Module first draft

Should I do a very quick first draft using modules? If so, are there any that offer a path to a custom component-level solution?  I doubt it.  I probably need to break down and admit the same thing that everyone else has: that the Digi-style smart ethernet connector, and the Xbee, are the best way to go for prototyping and even small volume production.  About $50 parts cost, or about $80 my sale price for one-off production.

If I go this route, I clearly will NOT make a single design for gateway and devices.