3D meshes can be morphed and merged just like any other model, image, dataset... in fact as DAZ was already mentioned, pretty sure that has a mesh morphing function in it somewhere.

And certainly human body models have hierarchical trees defining each major part (starts with torso, then e.g. pelvis, (crotch...) thigh, knee, shin, angle, foot, toes... or chest, (breasts..) shoulders, neck, head... etc), so why not have the ability to separate each one out and mix and match? So long as the attachment points survive and the bare ends can be morphed onto each other... maybe with some kind of hinting and resizing system... doesn't matter that it's hollow or with one-sided textures (so if you look from the inside out it's transparent), as the tubes are always closed up and the inside/outside orientation always preserved.