The first change is to add support for a new digital airspeed sensor from Measurement Specialities, the MS4525DO. The PX4 dev team announced this sensor recently, and I've been test flying it to ensure it works well with APM. It does! This new sensor is a huge advance over the analog sensors we've been using up to now.
The key difference is how low the thermal drift is in the reported differential pressure. A long standing problem with airspeed sensors has been the drift in the reading as the sensor warms up. This doesn't matter very much if you only need accurate airspeed readings at high speed as the contribution of thermal drift to airspeed drops rapidly with speed (as airspeed is proportional to the square root of the measured differential pressure). At lower speeds, such as when landing, it can matter, and having a sensor with low thermal drift is very nice. The I2C based MS4525D0 has internal temperature calibration to cope with thermal drift, which really helps.