Bind location of empty to vertex (after shapekeys) For a rather complex technical animation.
I need an empty to be locked to a vertex.
I cannot simply make create parent-root scenario, or use bones for this.
As the vertex is modified by complex animated shapekeys.
So how to achieve this ?
Well I found a solution, took me a while.
Since other people might get into this as well, here is the solution:

On the object with shapekey select a vertex, create a vertex group for it.
On the Empty use a Child-Of constraint, select the object and the new vertex group. 

Note its even possible this way to copy rotation of that vertex as well.