Ok, I had a go at this and I'll probably send this off for a prototype.
In the end, I omitted a number of headers, due to space considerations. I left the 1Wire data header, since it's not available on the 40-pin, and tucked a 3.5mm header row for screw terminals if the Moteino isn't populated.
I used dual SMD (1206) and 0.3" DIPs for all passives, which result in a board that is hand-solderable, but can also be reflowed (except 8P8C jacks, Moteino, and 40-pin connector, which are exclusively through-hole.
I modified my pinout on the first 8P8C so that it matches the most popular 1W adapter, the DS9490R, so all 1Wire devices designed for it on either 6P6C or 8P8C can be used, for example those by iButtonlink that are supported by OWFS. It also results in 1W and 5V/Gnd being on different pairs, minimizing capacitance, which can be a problem for 1Wire networks.
8ADC pins from the moteino (A0-A7) are shared with 8GPIO output pins on COM2 and COM3 8P8C. This allows you to decide what you want to read from where. I may swap a few of these out to correspond with interrupts or PWM on the Moteino, but for now it seems like ADC is probably the most valuable.
4 total of the GPIO/ADC inputs have optional pull-up and pull-down resistors. These will also allow monitoring Vcc by installing both as a voltage divider.
The SPI header is also in place, for use with SPI devices inside the enclosure, namely the CuPID indicator board (
http://www.cupidcontrols.com/2013/12/turn-on-the-spi-lights-spi-output-shift-registers-and-leds/).
Four DIO from the Moteino, DO-D3, are broken out on a header.
Happy to field questions.
Cheers,
Colin