image-spec v1.1.0-rc5 has just been released.
The changes related to ORAS include:

• Guidance for Artifacts Authors is introduced
• A decision tree is added in the Guidelines for Artifact Usage section in manifest.md
• String constants "index.json" and "blobs" are introduced
• MediaType became a required field in Descriptor

Change log between v1.1.0-rc4 and v1.1.0-rc5: opencontainers/image-spec@v1.1.0-rc4...v1.1.0-rc5