The Armalite, SAM3 32-bit "Arduino-Due-compatible" design

That looks awesome, but I doubt you could sell it at a price point that'd be interesting (< $49, say)

Compare to Raspberry Pi -- which has a lot more CPU power, but less I/O. However, I/O is easy to add with SPI/I2C expanders, and a $25 RPi plus a $25 I/O expander board would make a lot of sense.