it would be nice to be able to assign certain attributes to certain items so that they can react to other items based on speed, gravity, weight.
An example of this is a chracter on a horse. As the horse trots up and down, the riders upper torso, neck and head will react at different speeds based on how the master item is pulling or pushing against it.
Another simple is that of a chain, where each link reacts based on the movements of the parent item. In the case of chain, you could also assign gravity and weight, maybe even collision detection so that it can be animated in a more natural movement.
Here's a rough example.