It seems that there is currently no way to defer entity relation changes without a custom command buffer system. Additionally, there is no way to track relation changes via events or the EventRecorder. As of now, relations are almost useful, but these are some big caveats to have. If these features were in place, relations would be extremely useful for something like collisions. Having a collision enter and exit based on relation add / remove would be an effective way to tackle the problem.
It seems that there is currently no way to defer entity relation changes without a custom command buffer system. Additionally, there is no way to track relation changes via events or the EventRecorder. As of now, relations are almost useful, but these are some big caveats to have. If these features were in place, relations would be extremely useful for something like collisions. Having a collision enter and exit based on relation add / remove would be an effective way to tackle the problem.