I've been having a hard time drumming up architectural review on Handle entity references on import. I know it's pretty hard to see how the parts fit together, so I made a short video explaining the proposed approach.
The patch doesn't need code style review or manual testing yet, but instead needs architectural review to ensure we're building the right thing.
Also, for people who do want to start playing around with REST module based on this, keep in mind the following. Currently, only JSON-LD supports deserialization of incoming data, though there is an active issue to add support for JSON as well. Additionally, only EntityNG entities are supported, and I have only tested the entity_test bundle.
You can ask me any questions about the approach in IRC or over twitter.