Mask Editing By Vertex Group

I wish that we could mask editing by vertex group. This would be especially helpful for use with proportional editing and sculpting. The reason to use a vertex group is because this would allow granularity in the edit. Not only that, but it would be easier than using the mask brush in sculpt mode.

For example I was trying to elongate a shoe with proportional editing. The heel had a 'stand' (like high heels have) that I did not want to affect with proportional editing. If I were to elongate the shoe, it would either have to affect that which I didn't want (but still may or may not want it to affect other parts, hence why a vertex group would be helpful) or I would have to hide the vertices which I did, but then this causes the vertices that weren't hidden to have an obvious stop/start or split away if they were vertex/edge split.