Great ideas. I love the tiny tcp server thing in general. Would be great for all sorts of things, temp, humidity, security, streaming vid, two-way voice, etc. However, I am unclear why the 2 AA thing is focus here. I would think at that size, you could steal enouph power from the Ethernet cable or USB cable.
If you could make a HomePlug version, you have all the power you need so you have room for more features more flexible placement options - as a wedge device between bulb and outlet so you could place tiny "servers" in all your interior/exterior lights (for instance) for security and light management all reporting back to central controller in the house (i.e. Home Server).