A few issues covering some posts' points:
1) Shackles on the X don't prematurely flatten the leaves, that's an old wive's tale based upon the fact that leaves tend to flatten with age, and, off roading itself...and, pack INVERSION, which IS a problem, but not for the X....regardless of whether you have shackles or not. Long-term tests with and w/o shackles found that there was no difference, even though both tended to flatten with use/time. The use of overly LONG shackles is another story though, as if the shackles are SO LONG that they allow the leaf pack to bow UP, THAT'S a problem. Its more an issue on the old leaf sprung jeeps, etc...when they tried to get # -6" of SL from JUST a shackle, etc. Measurements on X's indicate that no one uses shackles to get that much lift, maybe 2" of lift at most...but not 6", etc. A shackle for the X would need to be ~ 8" longer than stock to get into inversion territory...and, most of our shackles are closer to ~ 3" longer to get 1.5" of lift, etc. Revolver Shackles can EXTEND to ~ 10.5", but, compress to barely longer than stock, so no inversion occurs....plus, they are easier on packs as they allow rotation and avoid stress from pack twisting, etc. (So don't worry about pack wear from lift shackles)
2) A bump stop extension robs you of uptravel, which is in short supply to start with on a lifted rig. The lift ITSELF is due to "Pre-Drooping" the suspension, so you use up some precious down travel just lifting. WITHOUT bumpstop extensions, the lost down travel is at least replaced by additional Up travel, but, stop extension rob you of that, so, you do not get any additional wheel travel, and in fact, can end up with LESS wheel travel/articulation.
3) The BL is best for preserving up travel, as its lifts the parts that the upcoming tire tends to whack.
4) As discussed, you get bucket bang w/o new UCA if you go over 2-2.5" of front lift.
5) The shocks with "built-in lift" essentially have built in bump stops that prevent the rig from settling to a lower ride height, thus robbing you of wheel travel.