Elasticsearch decay score based on occurrence
You cannot diversify elasticsearch sorting. You can only random_seed score the documents and hope for the best. You can use something like a top hits aggregator to aggregate buckets per author, but you cannot paginate a group of buckets. Therefore breaking pagination.
EDIT: before you downvote this answer just because it is Lucene related and not a real answer to the question: 1. ElasticSearch is Lucene-based 2. What the OP wants to do is really hard to do and I was just trying to help...
You could try to play around with decay from here:
However this doesn't allow for back-referencing on the previous hits of the current query (as a technique would need to match your use case)
I have encountered a similar problem to yours in a webapp that we used Lucene/Hibernate-Search for and I didn't really get a satisfying result and it still bothers me.
I think it is best to try to get a good user experience by trying to implement the ordering in another way.