I can imagine that no one has yet tried to run multiple things on the I2C bus and that one "driver" might interrupt the other which would be a bug. Certainly a worthy goal would be running multiple things on the I2C bus...
I haven't received my airspeed sensor yet, but I would imagine that simply setting up the sensor, including setting the correct sensor type would automatically make the PFD use that for speed/airspeed. @f5soh is the PFD guy and he could tell you the answer.