The roof rails you're referring to called "Hyper Roof Rails" by Nissan and they can be fitted as an aftermarket accessory and that is exactly what I have done with my T30.
You can also buy specific roof racks to suit the hyper roof rail design, but the carrying load capacity will reduce from 70Kg (for the standard type of roof racks) to 50Kg for the roof racks/cross bars that are fitted with the hyper roof rails.
The cross bar kit for the T31 xtrail with roof lights has this part number:
cross bar kit from Nissan, part no. KE732-JG010
As for the hyper roof rails with lights themselves, these are not cheap from Nissan and cost around $3000AUD (for the T30 model) so you can get an idea how much the T31 ones would cost. I have fitted aftermerket hyper roof rails on mine for quarter of that price and they look identical and even better than the genuine Nissan ones. (have a look in my website for pics or refer to the Aussie X-Trail Forum)