[dennyabraham]

iiuc, two resources can contain the same value, (http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch...) so you're not constrained by the number of identifiers with which you can reference a single entity. furthermore, it's debatable whether the versioned identifier hierarchy adheres to the principles of HATEOAS and discoverability, so practicality probably rules when implementing such an API.