uuids for entities are needed in Drupal 8 for content staging and other initiatives.
The generation and validation of uuids has already been implemented by dixon.
What's still missing is to implement the generation of uuid for each core entity.
Unknowing what was awaiting me, i've yesterday been conscripted by sun and fago for this task during the DrupalDevDays Barcelona code sprint(s).
Find (in a moment) below a patch against Drupal 8 dev branch of this morning with a first approach for implementing uuid in nodes for quick evaluation (before i continue with the other node types), including a uuid schema definition and updating in node.install, property definition in Node class and uuid generation in NodeStorageController, as well as a new entity_load_by_uuid function in entity.module.
If this (rather trivial) approach is okay, i continue with the other core entity types (terms, files, users, comments, probably not vocabularies, they already have a machine name).
Please review and comment as quick as possible <:)
PASSED: [[SimpleTest]]: [MySQL] 39,769 pass(es). View
FAILED: [[SimpleTest]]: [MySQL] Invalid PHP syntax in core/modules/system/system.install. View
PASSED: [[SimpleTest]]: [MySQL] 37,051 pass(es). View