This is looking great and will be a great addition to the Swift ecosystem. The integration with Swift-DocC looks really neat and is a great solution for ensuring that code snippets always build.
Could the proposal go into more detail into how you use API from other targets in the package? You mentioned in [Pitch] Swift Snippets - #34 by bitjammer that targets need to be imported, so I think the proposal should reflect that since this will be a common workflow.