I added the Princess Verachantesse style midriff rig to Monette Taida, and took several renders of her midriff to show how it looks. Normally renders of Monette will include more of her surfboard, but these were meant to show off the midriff. Look back in my Artstation post history to see more comprehensive images.
What we're looking at here is no shape keys and no weight painting of armature groups. Just Blender's parenting with automatic weights. The look is achieved by adding constrained bones to simulate muscle, fat, etc. It looks pretty good to my untrained eye!
Look back in my Artstation profile history to find posts about the rig itself on Princess Verachantesse and Giazelle Veloca, and links to Youtube to watch more. I believe I've put enough information out there for you to replicate these results on your own meshes.