@Scott: I have been trying to get my hands on the RPi compute module and re-design OSPi using the compute module. If this is feasible, it will allow LCD to be added to OSPi just like the Arduino-based OpenSprinkler. I am quite excited about this and hope it will happen soon!
I thought the same thing when I saw the compute module. It should allow for a much cleaner OSPi, although I thought it might increase your costs slightly. You have to include that SODIMM connector plus the USB/Ethernet ports on your board now.