As I said, he was only doing laps in an open park, so no cool shots yet! Even then VS often lost tracking if my quad went low enough to have contrasting backgrounds behind the bike. I can understand why it loses tracking, but I believe it shouldn't then pick some random shadow or tree trunk to track instead! That causes the quad to spin about which then makes it difficult to re-acquire the subject to re-establish tracking.
Another problem I am encountering is if the subject goes out of frame completely then VS doesn't acquire a new subject but it also doesn't 'relinquish' control so that that I can yaw and find my subject again. I have to switch to 'P' and back to 'F' to regain control.
ETA: Here is a quick upload showing VS switching subjects with possible 'interesting ' consequences: