UDOO looks good, but you might also look at the Beaglebone Black. both are sort of a Raspberry Pi + AVR on 1 board. At $45 (BBB) vs <$30 (Pi A + Atmel), it's probably not a cost improvement, but I'm waiting for mine for another project (fireworks controller via phone, 65 outputs of explosions) UDOO will be significantly more expensive. I'll also take texas instruments backing vs kickstarter.
A heatermeter 'cape' with all the I/O & LCD would be sweet too. It would be a nice, rectangular package for cases & could be easily swapped between projects. My heatermeter probably will see <5 uses per month, my fireworks controller <5 uses per year. multitasking the brains would be nice.
The BBB is pretty sweet and has tons more I/O, an ADC, hardware PWM so it could definitely take the place of the Atmel and the shift register on the HeaterMeter board. Integrated storage means no SD card needed either. It has a lot better physical design with the cape footprint as opposed to the Pi's "we just put some too-short headers on and good luck building a board around all the parts sticking up!"
Also to consider would be the Carambola 2 Atheros SoC with integrated wifi and storage. 1.1" x 1.5", USB host/slave, UART, SPI. You'd still need all the components of the HeaterMeter board but look at that size again. 1 inch by 1.5 inches! You could fit 6 of those in the rPi's footprint. Pulls 75mA @5V too at idle so it could be powered with a linear regulator off the 12V line pretty easily.
