Yes, you can expect the 4.0 in the Xterra too, but the Xterra and the Pathfinder will continue to be very different beasts. The Pathy offers 3rd-row seats, more luxury, probably a tad more power, and has independent rear suspension and a full-time transfer case is standard. The X may offer the full-time case as an option like the current Pathfinder (SE is part-time, LE is full-time) but hopefully that's the only concession to the soccer-mom crowd besides the lack of locking wheel hubs on the 4WD (like the current Pathy has been all along)
Brent