New documents may be branched from existing documents
The document may optionally have a "branchedFrom" versioned document ID and a "branchLabel" which would allow users to distinguish the purpose of their branch. Original documents will have neither. Users may remove (or maybe omit) branchedFrom and branchLabel from their document if they want their document to appear standalone.
The first change of the branch will include the changes of the other doc in the deps.
Collaborator Permissions
A document will have a new field which allows other users to edit the main view of the document.
Groups
Groups may begin referring to documents without a version ID, and the main view will be respected, including collaborators.
Breaking Changes
No breaking changes are necessary. Variant URLs will continue to work in the same way they do now, although they will be less necessary and might be deprecated in the future