A problem with this approach may come with locking. It won't be possible to store properties on bindings. You can't bind to a nonexistent resource. Agreed, this is true by definition. Down-level deletes make sense.
Bindings are part of the state of collection.
Judy will make a pass through the spec converting direct references to bindings. We will not include a definition of reference. We will define binding and redirect reference. Geoff thinks his distinction between mappings and bindings will help here. The introduction of a second binding for a collection could produce a forest of new mappings, but no new bindings.