We have implemented a wind estimation algorithm that also enables us to measure the airspeed without needing a sensor for that. It has been tested and works rather well.
However, it would be nice to have pressure altitude.
Most of the pins on CPU on the UAV DevBoard are already doing something, so there are not many options for interfacing. Really, there are only two ways you might do it:
1. I2C interface, using the clock and data pins on the ICSP. So you would have to share two of the pins between programming and interfacing to the pressure sensor. I think this is a reasonable way to go. The team is going to try to interface a magnetometer that way. If you go this route, you will have to do any debugging through the spare serial port.
2. Interface through the spare serial port.
Your best bet is probably I2C, because you could interface multiple sensors.