Exactly what NMTerras is saying. The lower center of gravity is one reason, but another reason is that he is planning on making this a kit, so this one is going to be the test-fit of all the parts and everything. It will basically be the exact same setup in the front as his Pathy but he wants to ensure it will fit an X. He is even going to be using the wheels and tires he has on his rig now in order to test it out to make sure it works exactly the same.
He wants it to resemble a stock X as much as possible when putting on the lift/SAS. That way when he does make this up as a kit, he can sell it outright and not have to have a disclaimer of "Will need to order 2 inch budy lift in order to make this work." He is planning to have it to where, with some minor-moderate fab work, this kit can be bought and put on any stock Xterra. Yes, there will need to be some fender trimming (not as much as you would think) and hacking off of some stock parts (where the IFS setup is/used to be), but besides that it should mostly be to where you put the parts/axle together, weld on the brackets and hoops, build the links, put up the coil overs and then hook everything up and do a spring-over-rear on the back axle. The majority of the cost in this is the axle. There are a few parts with this kit that will be fabbed by them and you won't be able to get anywhere else, but they are designed specifically for this application.
Eventually, maybe next winter, I would like to do a 4 link setup with coils in the rear, but that will take more custom work. Besides the obvious cutting out of the stock rear suspension and welding in new link brackets, the stock gas tank would have to be removed and a Pathfinder gas tank would have to be modified and fitted where the spare tire now resides in order to clear everything. This could cause some issues as there are quite a few sensors back in that area that, if done incorrectly, could cause some codes to be thrown.