I have been planning to have a look under my Xtrail (Top line ones now have HID low beam) Low beam is vastly better than the old D22 and my R51 (Older and non HID)
The simplest way for them to look at the headlight levelling I reckon would be suspension potentiometers on the anti roll bars, placed in the middle of each that would get you the average suspension height front and rear. The levelling itself looks to be done by a servo that changes the angle of the lamp inside the headlight housing.
I have been meaning to have a look at mine closely, I have HID low beam and a pair of halogens for high beam and high beam is reasonable but not great. If they use the same lamp assembly as a bi-xenon like the Ti Pathy there is a little motorised screen that blocks the light out at the top for low beam and flips away to allow the full pattern for high beam. It would be too much to ask for the Xtrail to have that type of lamp just without the high beam input to activate the screen and flip it out of the way! That would be easy to hook up to really bring up the high beam.