I just tried following the old 3.5 quick retopo tutorial (first discovered by Caruso the Painter), and while I can click add points, I can’t paint in retopo at all.
If I hold down shift and try to paint, nothing happens.
I just heard the first time of this retopo painting and gave it a try.
What it does here is simply repainting or erasing the old topology i already have.
So if this is what it should do it still works but I can’t see a practical use since you only get what you already had.
Now im sad because I almost believed there was some kind of magical way to do a retopo without headaches 
It was pretty good for when you wanted to add more geometry to an existing basemesh, without having to completely retopologize it from scratch.