I guess further idea's need confirmation of how far you intend to go lol
LMAO! You is just full of idea's lol - Well the glutes needs some tense and relaxed morphs
Really, the entire body needs tense and relaxed morphs. I was noticing it when I was doing a scene of one person holding a heavy weight. Having Flexions-On helps, but it's not really designed to show stress, especially when the muscle is elongated. Vascularity does somewhat more, but vascularity isn't muscle tissue.
Oh, and both glutes and breasts need morphs to make em flat, eg, when they're sitting/laying on a flat surface. hehe
Ironman13 did something like that for Anastasia, V4 and M4. A set of morphs called, appropriately enough, "Squish!" I don't know if those would work via GenX or not -- I don't have those sets -- and I expect it's better to have Genesis-native morphs in any event. (Also, judging from a couple of other products made to support Squish!, those morphs tend to screw up clothing fits, so that might need to be taken into account.)
The basic idea is you can control Up, Down, Left, Right, In & Out on each side of the breast and glute. With these combinations you will have full control of the movement.
I'm not sure about the glutes, but doesn't the pectoral bone supply a pretty good amount of that sort of control for the breast in Genesis? It won't squish them flat, but it'll do most of the rest, won't it?