I've start the same project using Android, basicly a smaller version of IOIO which only requires USB host mode. Also, have updated firmware so Android can now talk to the teensy 3.0. The main issues are:
- Basic loader for Android (Since IOIO is really just an I/O level operation, once the firmware is done, then, no need to really update)
- Common I/O protocol, there are several, IOIO, is one of many, but it is a basic protocol to communicate to get serial, I2C, PWM etc. So, the board is basicly a I/O interface via USB.
I've also been thinking of using i2c/USB , there is a spec now for this...