I obviously don't have a 4th gen, but I'd think a significant hurdle would be dealing with shocks for the X-Reas system, especially if you only replace 2 of the 4 shocks. I'd guess that would be a huge PITA just to figure out what to change if it can be changed. It would probably be quite a while before any aftermarket shock mfg'ers figure out longer shocks that can actually get incorporated into the X-Reas system.

Jeff
2000 4Runner SR5, supercharger, rear e-locker, ARB front locker, 285/75R16 MT/R's, custom bumpers & skids
2007 Tacoma double cab 4x4 - stock