I've been doing vertex attachment for a couple weeks, I call my macro "ConX". The act of doing it is pretty easy but implementing it for the user has been a challenge. The macro and FreeCAD software is rock solid at keeping things attached no matter if objects are in Part containers. The original code that started all this is in this post:
https://forum.freecadweb.org/viewtopic.php?f=22&t=64143, it shows how to get and place objects globally.
After I got the macro working I needed to know some angles for a stepping motor project so I took the macro in the direction of simulation (real rotation numbers).
You can see that I am rotating the pulleys by angle (the belt isn't moving). I then change the angle (by transform) of the Part base plate and all the objects follow. This is using a 1 millisec. timer to update. I made two models, pulley and base, then used simple copy for the duplication. All the objects are attached to vertex that are placed on the plate. I modify the sketch name to start with "LZ_" (landing zone) to denote a sketch with attachment vertex. All objects are placed using sketch vertex index values. This is very efficient if you have many object to place, for instance if I wanted to model a long stretch of wood rail fence.
There is no recompute during the sim, all it needs is a updateGui. I will post the macro as soon as I can resolve the user issues. It needs to be simple enough to use and explain.
before posting I tried attaching a body to a sketch endpoint and then move that endpoint and the body moved with it. Play around with the constraints in the sketch in this file (created with 0.19.3) and see for yourself how the body and part move with their corresponding vertex, I don't know what is that is not supported? 
can any dev confirm?