I have a quick question for you Nicolas Helleringer.

Elasticsearch lets you sort by distance between a point and a coordinate in a document through several methods. SLOPPY_ARC (default), ARC and PLANE. Do you think that is implementable directly via the Lucene Sort/SortField classes like you did DistanceSortField / DistanceComparator.
Is that worth it?
And what is the current implementation doing?

You can see elasticsearch doc in https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-sort.html#geo-sorting