Hi Dominque,
Yes I know what you are talking about. In Maya you can have a second mesh be the input of a shape key on the first mesh.
So it kind of works like a dynamic shape key. (This is sometimes called the Dorritto technique)
Sadly you cannot do this in Blender. Shape keys must be static.
Although, I’m pretty sure with the dependency graph changes in the recent versions of blender you can use the shrink wrap constraint and have it affect the same mesh (no need for a second mesh). However, I have only done some simple testing of this and have not tried it in production as yet.
I hope this makes sense. (especially the part about me not fully testing it yet haha)
