Symmetry between code on client and server has long been the promise of server-side JS. I'm working towards a similar goal of reusing Backbone's model/collection structure server-side. It does not attempt to pub/sub events to all clients with an instance of a model/collection, at least not yet.

My project simply proxies client fetch/save/destroy calls via Backbone.sync to the server. Through a RESTful URL convention and Express.js the model and collection of the client's request are recreated, any transformations applied and persisted, then sent back down the pipe. Server-side, models and collections extend their client-side bases and introduce additional functionality (i.e. per-user access control). Models and collections are not kept in memory server-side beyond the duration of a request.