@Joe: I think if you manage to do a nice weightmapping you can basically do anything. Weight maps cannot be mixed currently. I would need some testing, but I think, as long as you do not need to adopt the weightmaps when mixing figures you are fine. For making new cloth, I think that should work directly on the desired shape. I have to try it out. And yes, you are right, human growth is not directly linear. Custom sculpts can work out much nicer. But I still think one could collapse all into one or few dials.

Freeze the rig, yes, this a bit the idea, it depends on the details. Here, the script copies the K4 JCMs and blends them. There is no scaling involved, I was thinking that scaling is the same as animating the joint.

So yes, I think you can freeze everything except the weightmap. JCMs and Joint centers can be blended. Joint center erc can be pushed into the cloth so it follows, but you need something like Morphing Cloths or a manual sculpt to make a target morph.