Firstly, i used to dump feature requests a blenderstorm.org. Since it is gone, where can people post them these days:
I looked at the rigs from Big Buck Bunny where there is always one shape for enirely raised eyebrows. The shape is duplicated many times, each set to be multiplied by a different Vertex Group. So only one shape was modelled and split up into small chunks, saving work which is good.
But what if you want to change the brow shape afterwards? You have to change the main shape and update all other versions. Plus memory is wasted for multiple shapes that are really the same.
I think it would be great if you could assign multiple sliders to a shape, each having it’s own setting for a Vertex Group. It would save memory because and would be easier to manage/update (from the user point of view) since one is dealing with fewer shapes and can make changes faster. In many cases (when no overlapping shapes desired) the need of seperate L/R shapes would become redundant.