While the conversion to full CRUD for entities and classed objects for Drupal 8 made good progress, we’ve not yet reached the goals of fully translatable entities and having a default entity serialization for import/export, content staging and web services. For those points we need to know what’s in an entity! Yes we can look up the fields, but there are also base entity properties and further stuff modules put on entities, which both are no fields so we do not know anything about them.
That is what the new Entity Property API is supposed to change: It’s about providing a unified interface to entity properties *and* fields, avoiding the split between fields and non-field properties. So fields will be entity properties working with the same API as well! Then, it’s about being able to instrospect what’s going to be in an entity - regardless whether it has been added by a module or by the user via field UI. But furthermore, with classed entity objects as the basis we can improve the developer facing API and make it easier to access property and field values (I’m looking at you, $entity->field_body[LANGUAGE_NONE][‘value’]).
As we’ve outlined in the WSCCI Web Services Format Sprint report we want to have a modern OOP, interface based API for properties. The API should allow for introspection, so that it’s possible to look up the defined properties of an entity type in advance. If you know the Entity property information system of the Drupal 7 Entity module, it’s a bit similar to that, but instead of adding an extra layer above the existing entities it’s about supporting it natively. So there will be no need for entity wrappers - all the easy API and information will be directly available in $entity.
See the Entity Property API meta issue for a more complete list of planned features.