The definition of a small network is pretty much "single subnet". Yes, I understand very well that the average home of the future will have a mixed wiring. Of course, my own home does have Ethernet and Wi-Fi. In the not so distant future, it will have several Wi-Fi networks operating on different frequencies, some form of power-line networking, and some rooms may have their own high speed wireless wiring using UWB or some similar technology. But I am pretty much convinced that all of these will be organized as a single subnet.
You are remarkably trusting. You do all your homebanking on the same subnet as your teenage children who are studying Hacking 101 in the privacy of their bedroom? And when guests come over for dinner, you have no objection to them taking their laptop to the bathroom in order to surf for child porn over your wireless network. The fact is that a lot of people will WANT subnets in the home. They will want a router/firewall that will isolate each of the children's bedrooms so that they cannot mess with your bank account or with their brother's/sister's romantic chat sessions. Many people will want all wireless access to go through a router. Many will have an in-law suite, and want to seamlessly integrate their relative's existing network via a simple router connection. And the family jewels, that Raid 5 server cluster that holds all the family photos and videos, will be behind another router/firewall. When the kids host a LAN party, the gamers will connect to the family network via a router/firewall with limited Internet access for only the necessary protocols. Subnets multiply for architectural and security reasons. Multiple subnets per home is *NOT* a waste of anything. It is an invitation to dreamers and inventors to make better network things for the home market. It is an enabler of business activity, an enabler of competition. --Michael Dillon