It'd be cool to have a layered objects palette controlling a physics engine, so that the sim could be made to override or accomodate keyframed or captured motions.  Sometimes you want objects to interact naturally.  Other times, as an animator, you want unrealstic behaviour.  For example let's say you are staging a fight scene.  You animate/capture a figure kicking and apply a force modifier to his foot.  Now any time you call that animation it can physically affect other objects.  (It could even control like a game, with the motions applied to keypresses.)  You could walk around kicking anything in the environment and have it all react realistically.  Sometimes you wouldn't want that.  You might need the recipient of the kick to land in a certain place.  So you'd want to run the sim yet be able to tweak the outcome.  Or if you were controling a vehicle you may need to override the sim to cause a desired outcome, like tweaking a the sim so that the car crashes exactly through the glass...

Sorry, I tried to keep it figure-specific but drifted off into Bruckheimer territory.  Interesting stuff brewing here...