We need this for multiple use cases including GraphQL queries, HTTP APIs and more.
Andy Schaefer has written something using (extended) JSON schemas. Bertrand has been working on a prototype (ugly for now) for a remote content API, at https://github.com/apache/sling-whiteboard/tree/master/remote-content-api Older related discussions at https://cwiki.apache.org/confluence/x/2guQBQ
