Creating (and editing) a feature request from here: http://drupal.org/node/1472634#comment-6198780
I've been wishing for an API that gets much closer to a real Hypermedia API. To this end, I think a significant step forward for RestWS would be to make considered use of hypermedia controls within a standard hypermedia format, like Collection+JSON.
Hypermedia controls would indicate to the client what transitions are available and what protocol semantics are supported.
Doing this allows you to change all manner of characteristics of the API without breaking client code, so long as clients actually are using the API correctly (looking at rel and not making assumptions about semantics and URL structure).
I'm not sure how this would be done... I think it would mean abstracting from entity metadata rather than simply pushing it forward. Entity metadata could be used to discover possible transitions from any given representation. The presence of RDF mappings on an entity could help with this.