Be aware that if you remove the existing display from your X5 you will not be able to control and view all of the vehicle settings, trip computer, etc.

You will loose the total integration into Check Control display etc.
You will loose the antenna diversity feature
You will loose the TV (if fitted)

But otherwise I don't see a problem.
You have access to wheel speed pulses easily on the back of the instrument cluster or on the ABS unit
You'll have to run some antenna cables to the rear antennas (radio, TV if fitted, and GPS)
You'll have to run speaker cables to the rear to access the rear amp
You may need to run some heavier power cables - the ones for the screen are not designed for high current.