Revolver Shackles

Im not talking about desert/high speed stuff at all. Lets look at what makes the truck articulate and the limits. Im only gonna discuss rear suspension here. First is "up travel" or compression. This is limited by the factory bumpstop touching the frame. The other direction or extension or droop is limited by the shock itself. Now stock Frontiers use a shock with about 7.5" (shock is 21" extended, 13.5 compressed). Now for every inch more travel you need a 2" longer shock. We can also get a slightly longer shock in there do to the fact that the factory shock doesnt compress 100% at full bump. We are also going to excluded the fact that the spring will also limit articulation (typically compression). But lets say we run the longest Bilstein shocks that will fit with a mild 2-3" lift, these are 23.5" long and offer 8.5" of travel. Hardly enough travel to require more deflection than the factory spring will offer. BUT, lets assume you wanted to run 10" of wheel travel (still within the factory springs ability, or at least require removal of the overlaod), that would require you to lower the bottom shock mount and add'l 3" and you'd loose 3" of clearance under the lower shock mount that already hangs down. The only way to get a longer shock, that doesnt loose ground clearance, is to go up...through the bed.
This bring me back to the revolvers, and the fact that a tire needs to have weight on it for traction...why we love lockers. Even if you did get more articualtion from a shackle, unless you run a softer spring and more "up travel" you wont gain forward motion until you put LESS load on the compressed tire and more load on the etxtended tire. This is done with very soft springs and a ton of wheel travel (modern rock crawler stuff). Otherwise, a locker will basically do the same until the tread patch is overcome and you loose traction Now here's the kicker, you cna soften the springs to the point that they articulate all overthe place, but with limited wheel travel the vehicle would be nearly undrivable, and carrying any load would be out of the question.
One last thing. Because leaf springs act as a giant sway bar and pregressively reduce articulation as they twist, the revolvers or orbit eyes will actually allow the spring to compress (not extend) a bit more as the spring is not trying to twist itself. This is more of a byproduct of the revolvers design and the way it can rotate. You can also get similar results by running a narrower spring or bigger/softer spring bushings.