The new API should support:

• sort by relevance / score and doc id / indexorder
• sort by multiple fields
• do we need to express field type? We know it, no? What about non mapped fields?
• allow to pass custom comaprator (has to be script for ES)?
• support missing value (first, last, custom value when absent) => native Lucene seems to have more limitations on the custom value than ES.
• sort mode for multi values (min, max, avg, sum, median) => is it supported by native Lucene?
• reverse order
• sort by distance of a point (Coordinate and lat / long)
• sort by distance with custom distance computation (distance_type in ES), what about Lucene native?
• sort by distance from multiple points provided and multiple points in the documents (multi-value)? (that's ES)
• a way to back up to native Sort or Elasticsearch JSON "sort" for advanced use cases

Question:

• Why does ES has unit on distance sorting? How does that influence sorting?