I did this with my 2001 Frontier way back in 2003, but added the value of a lift, front LSD, and crawler gears in the t-case with the swap. I get the appeal since the truck is only a few years old and he probably is the only owner so he knows the history of it. My Frontier was a very straightforward swap with essentially all bolt-in components. Fast forward to modern trucks there are so many more electronic things that I would be concerned that there will be harness or computer issues beyond just the hardware. He would need to do a lot of research.
If he is not "invested" in the truck and simply wants a 4x4 (not building up for off-roading) then he is better trading it in for a 4x4. Band-aids like good tires, a locker, winch, etc all get you further down the trail before you get stuck, but ultimately you still get stuck...sometimes dangerously so and it will definitely make it more difficult to recover.
