The aim of the project is to create a system, based on services, which will make it possible to transparently use entities from a different site as local entities. I will base my system on Drupal 7, because the new APIs give me the required level of flexibility for the clean implementation. I will use the Entity API module to do easy CRUD on the entities.
Status: I am waiting for Relation or some other module to mature (because of the recursive cloning), and then I will integrate this module with it. After that, it will rock :) Also, UUIDs will probably in core for Drupal 8, which means that this module will be much smaller and powerful.