I like those ideas. I'm surprised the AA battery shield hasn't been made available. A AA battery shield with footprints for a bluetooth module would untether the arduino and allow OTA programming.
Sounds like you all like the ADC/DAC. I wonder when the xmega will be supported as it has adc and dacs onchip.
Here's something I was mocking up a while back. Its essentially an arduino uno clone with the atmega8u2 + atmega328 with standard .100" pitch sockets, so there is no need to have a separate "programmer" like the other tiny boards. It actually measures 0.5" x 1", the copper looking round thing is a US penny. Never built any since it seemed moot, just did it for fun.
Keep any ideas and suggestions coming. Ill start working on some shields and a site.