One of the requirements for the LSD initiative is that layouts themselves be editorial controlled. This means providing revisions to layouts with the ability to move the layout through an approval workflow.
I'm not proposing we put this functionality directly in core, but we provide a way for contrib to "easily" add the functionality.
In Drupal 7 this is achieved by attaching layout related settings to node and using the node revision system in conjunction with workflow modules (workbench, state_machine or workflow). This is the method panelizer, context fields (future version) and block references module use.
If we want to leverage the entity, we can use layouts within custom blocks or a new block plugin that links layouts with entities.
This is not a discussion on if the concept of revionable layouts in a single site is needed because it is. Saying "Just stick it in config/VCS" is not an acceptable answer either.
My goal is to begin discussion about how this would be possible. Once we have a little direction, I can open an issue for it.