...when you run over something, it can put them all back in place take a picture, and delete them all again.
What 3D Katamari did is discard the inner objects that have been covered by outer ones.
We could define size stages, when crossing the treshold discard objects not from the previous stage but the one before that, composite in canvas with the old canvas composite and draw with the objects from the previous stage.
You'd always have a somewhat blurred canvas center covered with sharp newer objects.
These newer objects are the ones that can be discarded on crashing. If you keep crashing there comes a time when nothing else can fall off.
I like this but I don't think I have the time for it :s