It looks like the first Galileo constellation may be coming on-line in the very near future. Some chipsets support it alonside existing GPS and some don't.

Any ideas if the P4 (or any DJI aircraft) will benefit?

http://www.esa.int/Our_Activitie ... lites_status_update

No ... the GPS units in the Phantom only receive GPS (Standard and P3-4K)  or GPS + Glonass (P3 Advanced and Pro, P4, Mavic, Inspire).

Sorry for waking up this very old thread....
What is stated here is actually only partially true...
I had a dead P4 Pro from work that I was able to fully tearout so I could get the GPS receiver. It's a u-blox M8030-KT : https://www.u-blox.com/en/product/ubx-m8030-series

The PCB exposes uart TX, RX terminals and using those with a uart to USB cable  I was able to hook it to u-blox software u-center and check the DJI configuration as well as actual capabilities of chip + antenna.

The chip is actually (I tested it) capable of using 3 out of 4 consttelaltions (GPS, GLONASS, GALILEO, BEIDOU) but only GPS + GLONASS is configured by DJI...

The chip is also SBAS capable with 3 possible levels (using range measurements, using integrity info, using ionospheric modelling broadcasted by SBAS). This capability is not used by DJI either.
u-blox also implemented special kalman filter settings (processing engine) for different dynamics lke pedestrian, automotive, airborne 1g, 2g, 4g, ... And once again DJI is not taking advantage of this feature.
DJI is also allowing 2D fixes... For flight safety, I would really only allow 3D fixes...

I think there is room for improvment with current hardware... I'm really wondering why DJI choosed not to enable the third constellation and tune gps settigns. I believe the only adverse effect would be the size of one of the output messages wich will grow. It is a message with detailled satellites info which is not needed anyway (all mandatory info to flight controller is on other messages which have fixed size wrt constellation selection)